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CHAPTER 22

The Package java.io

Input and output in Java is organized around the concept of streams. A stream is a sequence of items, usually 8-bit bytes, read or written over the course of time.

In the java.io package, all input is done through subclasses of the abstract class InputStream, and all output is done through subclasses of the abstract class OutputStream. The one exception to this rule is the class RandomAccessFile, which handles files that allow random access and perhaps intermixed reading and writing of the file.

For an input stream, the source of data might be a file, a String, an array of bytes, or bytes written to an output stream (typically by another thread). There are also "filter input streams" that take data from another input stream and transform or augment the data before delivering it as input. For example, a LineNumberInputStream passes bytes through verbatim but counts line terminators as they are read.

For an output stream, the sink of data might be a file, an array of bytes, or a buffer to be read as an input stream (typically by another thread). There are also "filter output streams" that transform or augment data before writing it to some other output stream.

An instance of class File represents a path name (a string) that might identify a particular file within a file system. Certain operations on the file system, such as renaming and deleting files, are done by this class rather than through streams.

An instance of class FileDescriptor represents an abstract indication of a particular file within a file system; such file descriptors are created internally by the Java I/O system.

There are two interfaces, DataInput and DataOutput, that support the transfer of data other than bytes or characters, such as long integers, floating-point numbers and strings. The class DataInputStream implements DataInput; the class DataOutputStream implements DataOutput; and RandomAccessFile implements both DataInput and DataOutput.

The class StreamTokenizer provides some simple support for parsing bytes or characters from an input stream into tokens such as identifiers, numbers, and strings, optionally ignoring comments and optionally recognizing or ignoring line terminators.

The hierarchy of classes defined in package java.io is as follows. (Classes whose names are shown here in boldface are in package java.io; the others are in package java.lang and are shown here to clarify subclass relationships.)

Object												§20.1				
	interface DataInput												§22.1
	interface DataOutput												§22.2
	InputStream												§22.3
		FileInputStream												§22.4
		PipedInputStream												§22.5
		ByteArrayInputStream												§22.6
		StringBufferInputStream												§22.7
		SequenceInputStream												§22.8
		FilterInputStream												§22.9
			BufferedInputStream												§22.10
			DataInputStream												§22.11
			LineNumberInputStream												§22.12
			PushBackInputStream												§22.13
	StreamTokenizer												§22.14
	OutputStream												§22.15
		FileOutputStream												§22.16
		PipedOutputStream												§22.17
		ByteArrayOutputStream												§22.18
		FilterOutputStream												§22.19
			BufferedOutputStream												§22.20
			DataOutputStream												§22.21
			PrintStream												§22.22
	RandomAccessFile												§22.23
	File												§22.24
	interface FileNameFilter												§22.25
	FileDescriptor												§22.26
	Throwable												§20.22
		Exception												§20.22
			IOException												§22.27
				EOFException												§22.28
				FileNotFoundException												§22.29
				InterruptedIOException												§22.30
				UTFDataFormatException												§22.31

22.1 The Interface java.io.DataInput

The DataInput interface provides for reading bytes from a binary stream and reconstructing from them data in any of the Java primitive types. There is also a facility for reconstructing a String from data in Java modified UTF-8 format.

The DataOutput interface (§22.2) supports the creation of binary output data suitable for reading back in through the DataInput interface.

The DataInput interface is implemented by classes DataInputStream (§22.11) and RandomAccessFile (§22.23).

public interface DataInput {
	public void readFully(byte[] b)
		throws IOException, NullPointerException;
	public void readFully(byte[] b, int off, int len)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public int skipBytes(int n) throws IOException;
	public boolean readBoolean() throws IOException;
	public byte readByte() throws IOException;
	public int readUnsignedByte() throws IOException;
	public short readShort() throws IOException;
	public int readUnsignedShort() throws IOException;
	public char readChar() throws IOException;
	public int readInt() throws IOException;
	public long readLong() throws IOException;
	public float readFloat() throws IOException;
	public double readDouble() throws IOException;
	public String readLine() throws IOException;
	public String readUTF() throws IOException;
}
It is generally true of all the reading routines in this interface that if end of file is reached before the desired number of bytes has been read, an EOFException (which is a kind of IOException) is thrown. If any byte cannot be read for any reason other than end of file, an IOException other than EOFException is thrown. In particular, an IOException may be thrown if the input stream has been closed (§22.3.6).

22.1.1 public void readFully(byte[] b)
throws IOException, NullPointerException;

The general contract of readFully(b) is that it reads some bytes from an input stream and stores them into the buffer array b. The number of bytes read is equal to the length of b.

This method blocks until one of the following conditions occurs:

If b is null, a NullPointerException is thrown.

If b.length is zero, then no bytes are read. Otherwise, the first byte read is stored into element b[0], the next one into b[1], and so on.

If an exception is thrown from this method, then it may be that some but not all bytes of b have been updated with data from the input stream.

22.1.2 public void readFully(byte[] b, int off, int len)
throws IOException, NullPointerException,
IndexOutOfBoundsException

The general contract of readFully(b, off, len) is that it reads len bytes from an input stream.

This method blocks until one of the following conditions occurs:

If b is null, a NullPointerException is thrown.

If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown.

If len is zero, then no bytes are read. Otherwise, the first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len.

If an exception is thrown from this method, then it may be that some but not all bytes of b in positions off through off+len-1 have been updated with data from the input stream.

22.1.3 public int skipBytes(int n) throws IOException

The general contract of skipBytes is that it makes an attempt to skip over n bytes of data from the input stream, discarding the skipped bytes. However, it may skip over some smaller number of bytes, possibly zero. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. This method never throws an EOFException. The actual number of bytes skipped is returned.

22.1.4 public boolean readBoolean() throws IOException;

The general contract of readBoolean is that it reads one input byte and returns true if that byte is nonzero, false if that byte is zero.

This method is suitable for reading the byte written by the writeBoolean method of interface DataOutput (§22.2.4).

22.1.5 public byte readByte() throws IOException

The general contract of readByte is that it reads and returns one input byte. The byte is treated as a signed value in the range -128 through 127, inclusive.

This method is suitable for reading the byte written by the writeByte method of interface DataOutput (§22.2.5).

22.1.6 public int readUnsignedByte() throws IOException

The general contract of readUnsignedByte is that it reads one input byte, zero- extends it to type int, and returns the result, which is therefore in the range 0 through 255.

This method is suitable for reading the byte written by the writeByte method of interface DataOutput (§22.2.5) if the argument to writeByte was intended to be a value in the range 0 through 255.

22.1.7 public short readShort() throws IOException

The general contract of readShort is that it reads two input bytes and returns a short value. Let a be the first byte read and b be the second byte. The value returned is: 

(short)((a << 8) | (b & 0xff))
This method is suitable for reading the bytes written by the writeShort method of interface DataOutput (§22.2.6).

22.1.8 public int readUnsignedShort() throws IOException

The general contract of readUnsignedShort is that it reads two input bytes and returns an int value in the range 0 through 65535. Let a be the first byte read and b be the second byte. The value returned is: 

(((a & 0xff) << 8) | (b & 0xff))
This method is suitable for reading the bytes written by the writeShort method of interface DataOutput (§22.2.6) if the argument to writeShort was intended to be a value in the range 0 through 65535.

22.1.9 public char readChar() throws IOException

The general contract of readChar is that it reads two input bytes and returns a char value. Let a be the first byte read and b be the second byte. The value returned is: 

(char)((a << 8) | (b & 0xff))
This method is suitable for reading bytes written by the writeChar method of interface DataOutput (§22.2.7).

22.1.10 public int readInt() throws IOException

The general contract of readInt is that it reads four input bytes and returns an int value. Let a be the first byte read, b be the second byte, c be the third byte, and d be the fourth byte. The value returned is: 


(((a & 0xff) << 24) | ((b & 0xff) << 16) |
  ((c & 0xff) <<    8) | (d & 0xff))
This method is suitable for reading bytes written by the writeInt method of interface DataOutput (§22.2.8).

22.1.11 public long readLong() throws IOException

The general contract of readLong is that it reads eight input bytes and returns a long value. Let a be the first byte read, b be the second byte, c be the third byte, d be the fourth byte, e be the fifth byte, f be the sixth byte, g be the seventh byte, and h be the eighth byte. The value returned is: 


(((long)(a & 0xff) << 56) |
  ((long)(b & 0xff) << 48) |
  ((long)(c & 0xff) <<  40) |
  ((long)(d & 0xff) << 32) |
  ((long)(e & 0xff) <<  24) |
  ((long)(f & 0xff) << 16) |
  ((long)(g & 0xff) <<    8) |
  ((long)(h & 0xff)))
This method is suitable for reading bytes written by the writeLong method of interface DataOutput (§22.2.9).

22.1.12 public float readFloat() throws IOException

The general contract of readFloat is that it reads four input bytes and returns a float value. It does this by first constructing an int value in exactly the manner of the readInt method (§22.1.10), then converting this int value to a float in exactly the manner of the method Float.intBitsToFloat (§20.9.23).

This method is suitable for reading bytes written by the writeFloat method of interface DataOutput (§22.2.10).

22.1.13 public double readDouble() throws IOException

The general contract of readDouble is that it reads eight input bytes and returns a double value. It does this by first constructing a long value in exactly the manner of the readlong method (§22.1.11), then converting this long value to a double in exactly the manner of the method Double.longBitsToDouble (§20.10.22).

This method is suitable for reading bytes written by the writeDouble method of interface DataOutput (§22.2.11).

22.1.14 public String readLine() throws IOException

The general contract of readLine is that it reads successive bytes, converting each byte separately into a character, until it encounters a line terminator or end of file; the characters read are then returned as a String. Note that because this method processes bytes, it does not support input of the full Unicode character set.

If end of file is encountered before even one byte can be read, then null is returned. Otherwise, each byte that is read is converted to type char by zero-extension. If the character '\n' is encountered, it is discarded and reading ceases. If the character '\r' is encountered, it is discarded and, if the following byte converts to the character '\n', then that is discarded also; reading then ceases. If end of file is encountered before either of the characters '\n' and '\r' is encountered, reading ceases. Once reading has ceased, a String is returned that contains all the characters read and not discarded, taken in order. Note that every character in this string will have a value less than \u0100, that is, (char)256.

22.1.15 public String readUTF() throws IOException

The general contract of readUTF is that it reads a representation of a Unicode character string encoded in Java modified UTF-8 format; this string of characters is then returned as a String.

First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the readUnsignedShort method (§22.1.8). This integer value is called the UTF length and specifies the number of additional bytes to be read. These bytes are then converted to characters by considering them in groups. The length of each group is computed from the value of the first byte of the group. The byte following a group, if any, is the first byte of the next group.

If the first byte of a group matches the bit pattern 0xxxxxxx (where x means "may be 0 or 1"), then the group consists of just that byte. The byte is zero-extended to form a character.

If the first byte of a group matches the bit pattern 110xxxxx, then the group consists of that byte a and a second byte b. If there is no byte b (because byte a was the last of the bytes to be read), or if byte b does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character:

(char)(((a & 0x1F) << 6) | (b & 0x3F))
If the first byte of a group matches the bit pattern 1110xxxx, then the group consists of that byte a and two more bytes b and c. If there is no byte c (because byte a was one of the last two of the bytes to be read), or either byte b or byte c does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character:

(char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))
If the first byte of a group matches the pattern 1111xxxx or the pattern 10xxxxxx, then a UTFDataFormatException is thrown.

If end of file is encountered at any time during this entire process, then an EOFException is thrown.

After every group has been converted to a character by this process, the characters are gathered, in the same order in which their corresponding groups were read from the input stream, to form a String, which is returned.

The writeUTF method of interface DataOutput (§22.2.14) may be used to write data that is suitable for reading by this method.

22.2 The Interface java.io.DataOutput

The DataOutput interface provides for converting data from any of the Java primitive types to a series of bytes and writing these bytes to a binary stream. There is also a facility for converting a String into Java modified UTF-8 format and writing the resulting series of bytes.

The DataInput interface (§22.1) can be used to read in and reconstruct Java data from the binary output data produced by the DataOutput interface.

The DataOutput interface is implemented by classes DataOutputStream (§22.21) and RandomAccessFile (§22.23).

public interface DataOutput {
	public void write(int b) throws IOException;
	public void write(byte[] b)
		throws IOException, NullPointerException;
	public void write(byte[] b, int off, int len)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public void writeBoolean(boolean v) throws IOException;
	public void writeByte(int v) throws IOException;
	public void writeShort(int v) throws IOException;
	public void writeChar(int v) throws IOException;
	public void writeInt(int v) throws IOException;
	public void writeLong(long v) throws IOException;
	public void writeFloat(float v) throws IOException;
	public void writeDouble(double v) throws IOException;
	public void writeBytes(String s)
		throws IOException, NullPointerException;
	public void writeChars(String s)
		throws IOException, NullPointerException;
	public void writeUTF(String s)
		throws IOException, NullPointerException;
}
For all the methods in this interface that write bytes, it is generally true that if a byte cannot be written for any reason, an IOException is thrown.

22.2.1 public void write(int b) throws IOException

The general contract for write is that one byte is written to the output stream. The byte to be written is the eight low-order bits of the argument b. The 24 high-order bits of b are ignored.

22.2.2 public void write(byte[] b)
throws IOException, NullPointerException

The general contract for write is that all the bytes in array b are written, in order, to the output stream.

If b is null, a NullPointerException is thrown.

If b.length is zero, then no bytes are written. Otherwise, the byte b[0] is written first, then b[1], and so on; the last byte written is b[b.length-1].

22.2.3 public void write(byte[] b, int off, int len)
throws IOException, NullPointerException, IndexOutOfBoundsException

The general contract for write is that len bytes from array b are written, in order, to the output stream.

If b is null, a NullPointerException is thrown.

If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown.

If len is zero, then no bytes are written. Otherwise, the byte b[off] is written first, then b[off+1], and so on; the last byte written is b[off+len-1].

22.2.4 public void writeBoolean(boolean v) throws IOException

The general contract for writeBoolean is that one byte is written to the output stream. If the argument v is true, the value (byte)1 is written; if v is false, the value (byte)0 is written.

The byte written by this method may be read by the readBoolean method of interface DataInput (§22.1.4), which will then return a boolean equal to v.

22.2.5 public void writeByte(int v) throws IOException

The general contract for writeByte is that one byte is written to the output stream to represent the value of the argument. The byte to be written is the eight low- order bits of the argument b. The 24 high-order bits of b are ignored. (This means that writeByte does exactly the same thing as write for an integer argument.)

The byte written by this method may be read by the readByte method of interface DataInput (§22.1.5), which will then return a byte equal to (byte)v.

22.2.6 public void writeShort(int v) throws IOException

The general contract for writeShort is that two bytes are written to the output stream to represent the value of the argument. The byte values to be written, in the order shown, are: 


(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readShort method of interface DataInput (§22.1.7), which will then return a short equal to (short)v.

22.2.7 public void writeChar(int v) throws IOException

The general contract for writeChar is that two bytes are written to the output stream to represent the value of the argument. The byte values to be written, in the order shown, are: 


(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readChar method of interface DataInput (§22.1.9), which will then return a char equal to (char)v.

22.2.8 public void writeInt(int v) throws IOException

The general contract for writeInt is that four bytes are written to the output stream to represent the value of the argument. The byte values to be written, in the order shown, are: 


(byte)(0xff & (v >> 24))
(byte)(0xff & (v >> 16))
(byte)(0xff & (v >>    8))
(byte)(0xff & v)
The bytes written by this method may be read by the readInt method of interface DataInput (§22.1.10), which will then return an int equal to v.

22.2.9 public void writeLong(long v) throws IOException

The general contract for writeLong is that four bytes are written to the output stream to represent the value of the argument. The byte values to be written, in the order shown, are: 


(byte)(0xff & (v >> 56))
(byte)(0xff & (v >> 48))
(byte)(0xff & (v >> 40))
(byte)(0xff & (v >> 32))
(byte)(0xff & (v >> 24))
(byte)(0xff & (v >> 16))
(byte)(0xff & (v >>    8))
(byte)(0xff & v)
The bytes written by this method may be read by the readLong method of interface DataInput (§22.1.11), which will then return a long equal to v.

22.2.10 public void writeFloat(float v) throws IOException

The general contract for writeFloat is that four bytes are written to the output stream to represent the value of the argument. It does this as if it first converts this float value to an int in exactly the manner of the Float.floatToIntBits method (§20.9.22) and then writes the int value in exactly the manner of the writeInt method (§22.2.8).

The bytes written by this method may be read by the readFloat method of interface DataInput (§22.1.12), which will then return a float equal to v.

22.2.11 public void writeDouble(double v) throws IOException

The general contract for writeDouble is that eight bytes are written to the output stream to represent the value of the argument. It does this as if it first converts this double value to a long in exactly the manner of the Double.doubleToLongBits method (§20.10.21) and then writes the long value in exactly the manner of the writeLong method (§22.2.9).

The bytes written by this method may be read by the readDouble method of interface DataInput (§22.1.13), which will then return a double equal to v.

22.2.12 public void writeBytes(String s)
throws IOException, NullPointerException

The general contract for writeBytes is that for every character in the string s, taken in order, one byte is written to the output stream.

If s is null, a NullPointerException is thrown.

If s.length is zero, then no bytes are written. Otherwise, the character s[0] is written first, then s[1], and so on; the last character written is s[s.length-1]. For each character, one byte is written, the low-order byte, in exactly the manner of the writeByte method (§22.2.5). The high-order eight bits of each character in the string are ignored.

22.2.13 public void writeChars(String s)
throws IOException, NullPointerException

The general contract for writeChars is that every character in the string s is written, in order, to the output stream, two bytes per character.

If s is null, a NullPointerException is thrown.

If s.length is zero, then no characters are written. Otherwise, the character s[0] is written first, then s[1], and so on; the last character written is s[s.length-1]. For each character, two bytes are actually written, high-order byte first, in exactly the manner of the writeChar method (§22.2.7).

22.2.14 public void writeUTF(String s)
throws IOException, NullPointerException

The general contract for writeUTF is that two bytes of length information are written to the output stream, followed by the Java modified UTF representation of every character in the string s.

If s is null, a NullPointerException is thrown.

Each character in the string s is converted to a group of one, two, or three bytes, depending on the value of the character.

If a character c is in the range '\u0001' through '\u007f', it is represented by one byte:

(byte)c
If a character c is '\u0000' or is in the range '\u0080' through '\u07ff', then it is represented by two bytes, to be written in the order shown:


(byte)(0xc0 | (0x1f & (c >> 6)))
(byte)(0x80 | (0x3f & c))
If a character c is in the range '\u0800' through '\uffff', then it is represented by three bytes, to be written in the order shown:


(byte)(0xc0 | (0x0f & (c >> 12)))
(byte)(0x80 | (0x3f & (c >>    6)))
(byte)(0x80 | (0x3f & c))
First, the total number of bytes needed to represent all the characters of s is calculated. If this number is larger than 65535, then a UTFDataFormatError is thrown. Otherwise, this length is written to the output stream in exactly the manner of the writeShort method (§22.2.6); after this, the one-, two-, or three-byte representation of each character in the string s is written.

The bytes written by this method may be read by the readUTF method of interface DataInput (§22.1.15), which will then return a String equal to s.

22.3 The Class java.io.InputStream

An input stream makes input bytes available from some source. 

public abstract class InputStream {
	public abstract int read() throws IOException;
	public int read(byte[] b)
	throws IOException, NullPointerException;
	public int read(byte[] b, int off, int len)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public long skip(long n) throws IOException;
	public int available() throws IOException;
	public void close() throws IOException;
	public void mark(int readlimit);
	public void reset() throws IOException;
	public boolean markSupported();
}

22.3.1 public abstract int read() throws IOException

The general contract of read is that it reads one byte from the input stream. The byte is returned as an integer in the range 0 to 255 (0x00-0xff). If no byte is available because the stream is at end of file, the value -1 is returned.

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If the byte cannot be read for any reason other than end of file, an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed (§22.3.6).

22.3.2 public int read(byte[] b)
throws IOException, NullPointerException

The general contract of read(b) is that it reads some number of bytes from the input stream and stores them into the buffer array b. The number of bytes actually read is returned as an integer.

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If b is null, a NullPointerException is thrown.

If the length of b is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[0], the next one into b[1], and so on. The number of bytes read is, at most, equal to the length of b. Let k be the number of bytes actually read; these bytes will be stored in elements b[0] through b[k-1], leaving elements b[k] through b[b.length-1] unaffected.

If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed (§22.15.5).

The read(b) method for class InputStream has the same effect as:

read(b, 0, b.length)

22.3.3 public int read(byte[] b, int off, int len)
throws IOException, NullPointerException,
IndexOutOfBoundsException

The general contract of read(b, off, len) is that it reads some number of bytes from the input stream and stores them into the buffer array b. An attempt is made to read as many as len bytes, but a smaller number may be read, possibly zero. The number of bytes actually read is returned as an integer.

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If b is null, a NullPointerException is thrown.

If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown.

If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len. Let k be the number of bytes actually read; these bytes will be stored in elements b[off] through b[off+k-1], leaving elements b[off+k] through b[off+len-1] unaffected.

In every case, elements b[0] through b[off] and elements b[off+len] through b[b.length-1] are unaffected.

If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed (§22.15.5).

The read(b, off, len) method for class InputStream simple calls the method read() repeatedly. If the first such call results in an IOException, that exception is returned from the call to the read(b, off, len) method. If any subsequent call to read() results in a IOException, the exception is caught and treated as if it were end of file; the bytes read up to that point are stored into b and the number of bytes read before the exception occurred is returned.

22.3.4 public long skip(long n) throws IOException

The general contract of skip is that it makes an attempt to skip over n bytes of data from the input stream, discarding the skipped bytes. However, it may skip over some smaller number of bytes, possibly zero. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. The actual number of bytes skipped is returned.

22.3.5 public int available() throws IOException

The general contract of available is that it returns an integer k; the next caller of a method for this input stream, which might be the same thread or another thread, can then expect to be able to read or skip up to k bytes without blocking (waiting for input data to arrive).

The available method for class InputStream always returns 0.

22.3.6 public int close() throws IOException

The general contract of close is that it closes the input stream. A closed stream cannot perform input operations and cannot be reopened.

The close method for class InputStream does nothing and simply returns.

22.3.7 public void mark(int readlimit)

The general contract of mark is that, if the method markSupported returns true, the stream somehow remembers all the bytes read after the call to mark and stands ready to supply those same bytes again if and whenever the method reset is called. However, the stream is not required to remember any data at all if more than readlimit bytes are read from the stream before reset is called.

The mark method for class InputStream does nothing.

22.3.8 public void reset() throws IOException

The general contract of reset is:

The method reset for class InputStream always throws an IOException.

22.3.9 public boolean markSupported()

The general contract of markSupported is that if it returns true, then the stream supports the mark (§22.3.7) and reset (§22.3.8) operations. For any given instance of InputStream, this method should consistently return the same truth value whenever it is called.

The markSupported method for class InputStream returns false.

22.4 The Class java.io.FileInputStream

A file input stream obtains input bytes from a file in a file system. What files are available depends on the host environment. 

public class FileInputStream extends InputStream  {
	public FileInputStream(String path)
		throws SecurityException, FileNotFoundException;
	public FileInputStream(File file)
		throws SecurityException, FileNotFoundException;
	public FileInputStream(FileDescriptor fdObj)
		throws SecurityException;
	public native int read() throws IOException;
	public int read(byte[] b)
		throws IOException, NullPointerException;
	public int read(byte[] b, int off, int len)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public native long skip(long n) throws IOException;
	public native int available() throws IOException;
	public native void close() throws IOException;
	public final FileDescriptor getFD() throws IOException;
	protected void finalize() throws IOException;
}

22.4.1 public FileInputStream(String path)
throws SecurityException, FileNotFoundException

This constructor initializes a newly created FileInputStream by opening a connection to an actual file, the file named by the path name path in the file system. A new FileDescriptor object is created to represent this file connection.

First, if there is a security manager, its checkRead method (§20.17.19) is called with the path argument as its argument.

If the actual file cannot be opened, a FileNotFoundException is thrown.

22.4.2 public FileInputStream(File file)
throws SecurityException, FileNotFoundException

This constructor initializes a newly created FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system. A new FileDescriptor object is created to represent this file connection.

First, if there is a security manager, its checkRead method (§20.17.19) is called with the path represented by the file argument as its argument.

If the actual file cannot be opened, a FileNotFoundException is thrown.

22.4.3 public FileInputStream(FileDescriptor fdObj)
throws SecurityException

This constructor initializes a newly created FileInputStream by using the file descriptor fdObj, which represents an existing connection to an actual file in the file system.

First, if there is a security manager, its checkRead method (§20.17.18) is called with the file descriptor fdObj as its argument.

22.4.4 public final FileDescriptor getFD() throws IOException

This method returns the FileDescriptor object (§22.26) that represents the connection to the actual file in the file system being used by this FileInputStream.

22.4.5 public int read() throws IOException;

The byte for this operation is read from the actual file with which this file input stream is connected.

Implements the read method of InputStream (§22.3.1).

22.4.6 public int read(byte[] b)
throws IOException, NullPointerException

Bytes for this operation are read from the actual file with which this file input stream is connected.

Overrides the read method of InputStream (§22.3.2).

22.4.7 public int read(byte[] b, int off, int len)
throws IOException, NullPointerException, IndexOutOfBoundsException

Bytes for this operation are read from the actual file with which this file input stream is connected.

Overrides the read method of InputStream (§22.3.3).

22.4.8 public long skip(long n) throws IOException

Bytes for this operation are read from the actual file with which this file input stream is connected.

Overrides the skip method of InputStream (§22.3.4).

22.4.9 public int available() throws IOException

Overrides the available method of InputStream (§22.3.5).

22.4.10 public void close() throws IOException

This file input stream is closed and may no longer be used for reading bytes.

Overrides the close method of InputStream (§22.3.6).

22.4.11 protected void finalize() throws IOException

A FileInputStream uses finalization to clean up the connection to the actual file.

22.5 The Class java.io.PipedInputStream

A piped input stream should be connected to a piped output stream; the piped input stream then provides whatever data bytes are written to the piped output stream. Typically, data is read from a PipedInputStream object by one thread and data is written to the corresponding PipedOutputStream (§22.17) by some other thread. Attempting to use both objects from a single thread is not recommended, as it may deadlock the thread. The piped input stream contains a buffer, decoupling read operations from write operations, within limits. 

public class PipedInputStream extends InputStream {
	public PipedInputStream(PipedOutputStream src)
		throws IOException;
	public PipedInputStream();
	public void connect(PipedOutputStream src)
		throws IOException;
	public int read() throws IOException;
	public int read(byte[] b, int off, int len) 
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public void close() throws IOException;
}

22.5.1 public PipedInputStream(PipedOutputStream src)
throws IOException

This constructor initializes a newly created PipedInputStream so that it is connected to the piped output stream src. Data bytes written to src will then be available as input from this stream.

22.5.2 public PipedInputStream()

This constructor initializes a newly created PipedInputStream so that it is not yet connected. It must be connected to a PipedOutputStream before being used.

22.5.3 public void connect(PipedOutputStream src)
throws IOException

The connect method causes this piped input stream to be connected to the piped output stream src. If this object is already connected to some other piped output stream, an IOException is thrown.

If src is an unconnected piped output stream and snk is an unconnected piped input stream, they may be connected by either the call:

snk.connect(src)
or the call: 

src.connect(snk)
The two calls have the same effect.

22.5.4 public int read() throws IOException

If a thread was providing data bytes to the connected piped output stream, but the thread is no longer alive, then an IOException is thrown.

Implements the read method of InputStream (§22.3.1).

22.5.5 public int read(byte[] b, int off, int len)
throws IOException, NullPointerException, IndexOutOfBoundsException

If a thread was providing data bytes to the connected piped output stream, but the thread is no longer alive, then an IOException is thrown.

Overrides the read method of InputStream (§22.3.3).

22.5.6 public void close() throws IOException

This piped input stream is closed and may no longer be used for reading bytes.

Overrides the close method of InputStream (§22.3.6).

22.6 The Class java.io.ByteArrayInputStream

A ByteArrayInputStream contains an internal buffer that contains bytes that may be read from the stream. An internal counter keeps track of the next byte to be supplied by the read method. See also StringBufferInputStream (§22.7). 

public class ByteArrayInputStream extends InputStream {
	protected byte[] buf;
	protected int pos;
	protected int count;
	public ByteArrayInputStream(byte[] buf);
	public ByteArrayInputStream(byte[] buf,
			int offset, int length);
	public int read()
		throws NullPointerException, IndexOutOfBoundsException;
	public int read(byte[] b, int off, int len)
		throws NullPointerException, IndexOutOfBoundsException;
	public long skip(long n);
	public int available();
	public void reset();
}

22.6.1 protected byte[] buf;

An array of bytes that was provided by the creator of the stream. Elements buf[0] through buf[count-1] are the only bytes that can ever be read from the stream; element buf[pos] is the next byte to be read.

22.6.2 protected int pos;

This value should always be nonnegative and not larger than the value of count. The next byte to be read from this stream will be buf[pos].

22.6.3 protected int count;

This value should always be nonnegative and not larger than the length of buf. It is one greater than the position of the last byte within buf that can ever be read from this stream.

22.6.4 public ByteArrayInputStream(byte[] buf)

This constructor initializes a newly created ByteArrayInputStream so that it uses buf as its buffer array. The initial value of pos is 0 and the initial value of count is the length of buf.

22.6.5 public ByteArrayInputStream(byte[] buf,
int offset, int length)

This constructor initializes a newly created ByteArrayInputStream so that it uses buf as its buffer array. The initial value of pos is offset and the initial value of count is offset+len.

Note that if bytes are simply read from the resulting input stream, elements buf[pos] through buf[pos+len-1] will be read; however, if a reset operation (§22.6.10) is performed, then bytes buf[0] through buf[pos-1] will then become available for input.

22.6.6 public int read()
throws NullPointerException, IndexOutOfBoundsException

If pos equals count, then -1 is returned to indicate end of file. Otherwise, the value buf[pos]&0xff is returned; just before the return, pos is incremented by 1.

Implements the read method of InputStream (§22.3.1).

22.6.7 public int read(byte[] b, int off, int len)
throws NullPointerException, IndexOutOfBoundsException

If pos equals count, then -1 is returned to indicate end of file. Otherwise, the number k of bytes read is equal to the smaller of len and count-pos. If k is positive, then bytes buf[pos] through buf[pos+k-1] are copied into b[off] through b[off+k-1] in the manner performed by System.arraycopy (§20.18.16). The value k is added into pos and k is returned.

Overrides the read method of InputStream (§22.3.3).

22.6.8 public long skip(long n)

The actual number k of bytes to be skipped is equal to the smaller of n and count-pos. The value k is added into pos and k is returned.

Overrides the skip method of InputStream (§22.3.4).

22.6.9 public int available()

The quantity count-pos is returned.

Overrides the available method of InputStream (§22.3.5).

22.6.10 public void reset()

The value of pos is set to 0.

Overrides the reset method of InputStream (§22.3.8).

22.7 The Class java.io.StringBufferInputStream

A StringBufferInputStream contains an internal buffer that contains bytes that may be read from the stream. An internal counter keeps track of the next byte to be supplied by the read method. See also ByteArrayInputStream (§22.6). 

public class StringBufferInputStream extends InputStream {
	protected String buffer;
	protected int pos;
	protected int count;
	public StringBufferInputStream(String s)
		throws NullPointerException;
	public int read();
	public int read(byte[] b, int off, int len)
		throws NullPointerException, IndexOutOfBoundsException;
	public long skip(long n);
	public int available();
	public void reset();
}
Note that bytes read from a StringBufferInputStream are the low-order eight bits of each character in the string; the high-order eight bits of each character are ignored.

22.7.1 protected String buffer;

A String that was provided by the creator of the stream. Elements buffer[0] through buffer[count-1] are the only bytes that can ever be read from this stream; element buffer[pos] is the next byte to be read.

22.7.2 protected int pos;

This value should always be nonnegative and not larger than the value of count. The next byte to be read from this stream will be buffer[pos].

22.7.3 protected int count;

This value equals the length of buffer. It is the number of bytes of data in buffer that can ever be read from this stream.

22.7.4 public StringBufferInputStream(String s)
throws NullPointerException

This constructor initializes a newly created StringBufferInputStream so that it uses s as its buffer array. The initial value of pos is 0 and the initial value of count is the length of buffer.

22.7.5 public int read()

If pos equals count, then -1 is returned to indicate end of file. Otherwise, the value buffer[pos]&0xff is returned; just before the return, 1 is added to pos.

Implements the read method of InputStream (§22.3.1).

22.7.6 public int read(byte[] b, int off, int len)
throws NullPointerException, IndexOutOfBoundsException

If pos equals count, then -1 is returned to indicate end of file. Otherwise, the number k of bytes read is equal to the smaller of len and count-pos. If k is positive, then bytes buffer[pos] through buffer[pos+k-1] are copied into b[off] through b[off+k-1] in the manner performed by System.arraycopy (§20.18.16). The value k is added into pos and k is returned.

Overrides the read method of InputStream (§22.3.3).

22.7.7 public long skip(long n)

The actual number k of bytes to be skipped is equal to the smaller of n and count-pos. The value k is added into pos and k is returned.

Overrides the skip method of InputStream (§22.3.4).

22.7.8 public int available()

The quantity count-pos is returned.

Overrides the available method of InputStream (§22.3.5).

22.7.9 public void reset()

The value of pos is set to 0.

Overrides the reset method of InputStream (§22.3.8).

22.8 The Class java.io.SequenceInputStream

A SequenceInputStream represents the logical concatenation of other input streams. It starts out with an ordered collection of input streams and reads from the first one until end of file is reached, whereupon it reads from the second one, and so on, until end of file is reached on the last of the contained input streams. 

public class SequenceInputStream extends InputStream {
	public SequenceInputStream(Enumeration e);
	public SequenceInputStream(InputStream s1, InputStream s2);
	public int read() throws IOException;
	public int read(byte[] buf, int pos, int len)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public void close() throws IOException;
}

22.8.1 public SequenceInputStream(Enumeration e)

This constructor initializes a newly created SequenceInputStream by remembering the argument, which must be an Enumeration (§21.1) that produces objects whose run-time type is InputStream (§22.3). The input streams that are produced by the enumeration will be read, in order, to provide the bytes to be read from this SequenceInputStream. After each input stream from the enumeration is exhausted, it is closed by calling its close method.

22.8.2 public SequenceInputStream(InputStream s1,
InputStream s2)

This constructor initializes a newly created SequenceInputStream by remembering the two arguments, which will be read in order, first s1 and then s2, to provide the bytes to be read from this SequenceInputStream.

22.8.3 public int read() throws IOException

Implements the read method of InputStream (§22.3.1).

22.8.4 public int read(byte[] buf, int pos, int len)
throws IOException, NullPointerException, IndexOutOfBoundsException

Overrides the read method of InputStream (§22.3.3).

22.8.5 public void close() throws IOException

This SequenceInputStream is closed. A closed SequenceInputStream cannot perform input operations and cannot be reopened.

If this stream was created from an enumeration, all remaining elements are requested from the enumeration and closed before the close method returns.

Overrides the close method of InputStream (§22.3.6).

22.9 The Class java.io.FilterInputStream

A FilterInputStream contains some other input stream, which it uses as its basic source of data, possibly transforming the data along the way or providing additional functionality. The class FilterInputStream itself simply overrides all methods of InputStream with versions that pass all requests to the contained input stream. Subclasses of FilterInputStream may further override some of these methods and may also provide additional methods and fields. 

public class FilterInputStream extends InputStream {
	protected InputStream in;
	protected FilterInputStream(InputStream in);
	public int read() throws IOException;
	public int read(byte[] b)
		throws IOException, NullPointerException;
	public int read(byte[] b, int off, int len)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public long skip(long n) throws IOException;
	public int available() throws IOException;
	public void close() throws IOException;
	public void mark(int readlimit);
	public void reset() throws IOException;
	public boolean markSupported();
}

22.9.1 protected InputStream in;

The input stream to be filtered.

22.9.2 protected FilterInputStream(InputStream in)

This constructor initializes a newly created FilterInputStream by assigning the argument in to the field this.in so as to remember it for later use.

22.9.3 public int read() throws IOException

This method simply performs in.read() and returns the result.

Implements the read method of InputStream (§22.3.1).

22.9.4 public int read(byte[] b)
throws IOException, NullPointerException

This method simply performs the call read(b, 0, b.length) and returns the result. It is important that it does not do in.read(b) instead; certain subclasses of FilterInputStream depend on the implementation strategy actually used.

Overrides the read method of InputStream (§22.3.2).

22.9.5 public int read(byte[] b, int off, int len)
throws IOException, NullPointerException, IndexOutOfBoundsException

This method simply performs in.read(b, off, len) and returns the result.

Overrides the read method of InputStream (§22.3.3).

22.9.6 public long skip(long n) throws IOException

This method simply performs in.skip() and returns the result.

Overrides the skip method of InputStream (§22.3.4).

22.9.7 public int available() throws IOException

This method simply performs in.available() and returns the result.

Overrides the available method of InputStream (§22.3.5).

22.9.8 public void close() throws IOException

This method simply performs in.close().

Overrides the close method of InputStream (§22.3.6).

22.9.9 public void mark(int readlimit)

This method simply performs in.mark().

Overrides the mark method of InputStream (§22.3.7).

22.9.10 public void reset() throws IOException

This method simply performs in.reset().

Overrides the reset method of InputStream (§22.3.8).

22.9.11 public boolean markSupported()

This method simply performs in.markSupported() and returns whatever value is returned from that invocation.

Overrides the markSupported method of InputStream (§22.3.9).

22.10 The Class java.io.BufferedInputStream

A BufferedInputStream adds functionality to another input stream-namely, the ability to buffer the input and to support the mark and reset methods. When the BufferedInputStream is created, an internal buffer array is created. As bytes from the stream are read or skipped, the internal buffer is refilled as necessary from the contained input stream, many bytes at a time. The mark operation remembers a point in the input stream and the reset operation causes all the bytes read since the most recent mark operation to be reread before new bytes are taken from the contained input stream. 

public class BufferedInputStream extends FilterInputStream {
	protected byte[] buf;
	protected int count = 0;
	protected int pos = 0;
	protected int markpos = -1;
	protected int marklimit = 0;
	public BufferedInputStream(InputStream in);
	public BufferedInputStream(InputStream in, int size);
	public int read() throws IOException;
	public int read(byte[] b)
		throws IOException, NullPointerException;
	public int read(byte[] b, int off, int len)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public long skip(long n) throws IOException;
	public int available() throws IOException;
	public void mark(int readlimit);
	public void reset() throws IOException;
	public boolean markSupported();
}

22.10.1 protected byte[] buf;

The internal buffer array. When necessary, it may be replaced by another array of a different size.

22.10.2 protected int count = 0;

This value is always in the range 0 through buf.length; elements buf[0] through buf[count-1] contain buffered input data obtained from the underlying input stream.

22.10.3 protected int pos = 0;

This value is always in the range 0 through count. If it is less than count, then buf[pos] is the next byte to be supplied as input; if it is equal to count, then the next read or skip operation will require more bytes to be read from the contained input stream.

22.10.4 protected int markpos = -1;

This value is always in the range -1 through pos. If there is no marked position in the input stream, this field is -1. If there is a marked position in the input stream, then buf[markpos] is the first byte to be supplied as input after a reset operation. If markpos is not -1, then all bytes from positions buf[markpos] through buf[pos-1] must remain in the buffer array (though they may be moved to another place in the buffer array, with suitable adjustments to the values of count, pos, and markpos); they may not be discarded unless and until the difference between pos and markpos exceeds marklimit.

22.10.5 protected int marklimit;

Whenever the difference between pos and markpos exceeds marklimit, then the mark may be dropped by setting markpos to -1.

22.10.6 public BufferedInputStream(InputStream in)

This constructor initializes a newly created BufferedInputStream by saving its argument, the input stream in, for later use. An internal buffer array is created and stored in buf.

22.10.7 public BufferedInputStream(InputStream in, int size)

This constructor initializes a newly created BufferedInputStream by saving its argument, the input stream in, for later use. An internal buffer array of length size is created and stored in buf.

22.10.8 public int read() throws IOException

See the general contract of the read method of InputStream (§22.3.1).

Overrides the read method of FilterInputStream (§22.9.3).

22.10.9 public int read(byte[] b)
throws IOException, NullPointerException

See the general contract of the read method of InputStream (§22.3.2).

Overrides the read method of FilterInputStream (§22.9.4).

22.10.10 public int read(byte[] b, int off, int len)
throws IOException, NullPointerException, IndexOutOfBoundsException

See the general contract of the read method of InputStream (§22.3.3).

Overrides the read method of FilterInputStream (§22.9.5).

22.10.11 public long skip(long n) throws IOException

See the general contract of the skip method of InputStream (§22.3.4).

Overrides the skip method of FilterInputStream (§22.9.6).

22.10.12 public int available() throws IOException

See the general contract of the available method of InputStream (§22.3.5).

Overrides the available method of FilterInputStream (§22.9.7).

22.10.13 public void mark(int readlimit)

The field marklimit is set equal to the argument and markpos is set equal to pos

Overrides the mark method of FilterInputStream (§22.9.9).

22.10.14 public void reset() throws IOException

See the general contract of the reset method of InputStream (§22.3.8).

If markpos is -1 (no mark has been set or the mark has been invalidated), an IOException is thrown. Otherwise, pos is set equal to markpos.

Overrides the reset method of FilterInputStream (§22.9.10).

22.10.15 public boolean markSupported()

This method returns true (a BufferedInputStream always supports mark).

Overrides the markSupported method of FilterInputStream (§22.9.11).

22.11 The Class java.io.DataInputStream

A data input stream provides facilities for reading bytes from an input source and interpreting specific character sequences as representing data of diverse types. 

public class DataInputStream extends FilterInputStream
		implements DataInput {
	public DataInputStream(InputStream in);
	public final void readFully(byte[] b)
		throws IOException, NullPointerException;
	public final void readFully(byte[] b, int off, int len)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public final int skipBytes(int n) throws IOException;
	public final boolean readBoolean() throws IOException;
	public final byte readByte() throws IOException;
	public final int readUnsignedByte() throws IOException;
	public final short readShort() throws IOException;
	public final int readUnsignedShort() throws IOException;
	public final char readChar() throws IOException;
	public final int readInt() throws IOException;
	public final long readLong() throws IOException;
	public final float readFloat() throws IOException;
	public final double readDouble() throws IOException;
	public final String readLine() throws IOException;
	public final String readUTF() throws IOException;
	public final static String readUTF(DataInput in)
		throws IOException;
}

22.11.1 public DataInputStream(InputStream in)

This constructor initializes a newly created DataInputStream by saving its argument, the input stream in, for later use.

22.11.2 public final void readFully(byte[] b)
throws IOException, NullPointerException

See the general contract of the readFully method of DataInput (§22.1.1).

Bytes for this operation are read from the contained input stream.

22.11.3 public final void readFully(byte[] b, int off, int len)
throws IOException, NullPointerException, IndexOutOfBoundsException

See the general contract of the readFully method of DataInput (§22.1.2).

Bytes for this operation are read from the contained input stream.

22.11.4 public final int skipBytes(int n) throws IOException

See the general contract of the skipBytes method of DataInput (§22.1.3).

Bytes for this operation are read from the contained input stream.

22.11.5 public final boolean readBoolean() throws IOException

See the general contract of the readBoolean method of DataInput (§22.1.4).

The byte for this operation is read from the contained input stream.

22.11.6 public final byte readByte() throws IOException

See the general contract of the readByte method of DataInput (§22.1.5).

The byte for this operation is read from the contained input stream.

22.11.7 public final int readUnsignedByte() throws IOException

See the general contract of the readUnsignedByte method of DataInput (§22.1.6).

The byte for this operation is read from the contained input stream.

22.11.8 public final short readShort() throws IOException

See the general contract of the readShort method of DataInput (§22.1.7).

Bytes for this operation are read from the contained input stream.

22.11.9 public final int readUnsignedShort() throws IOException

See the general contract of the readUnsignedShort method of DataInput (§22.1.8).

Bytes for this operation are read from the contained input stream.

22.11.10 public final char readChar() throws IOException

See the general contract of the readChar method of DataInput (§22.1.9).

Bytes for this operation are read from the contained input stream.

22.11.11 public final int readInt() throws IOException

See the general contract of the readInt method of DataInput (§22.1.10).

Bytes for this operation are read from the contained input stream.

22.11.12 public final long readLong() throws IOException

See the general contract of the readLong method of DataInput (§22.1.11).

Bytes for this operation are read from the contained input stream.

22.11.13 public final float readFloat() throws IOException

See the general contract of the readFloat method of DataInput (§22.1.12).

Bytes for this operation are read from the contained input stream.

22.11.14 public final double readDouble() throws IOException

See the general contract of the readDouble method of DataInput (§22.1.13).

Bytes for this operation are read from the contained input stream.

22.11.15 public final String readLine() throws IOException

See the general contract of the readLine method of DataInput (§22.1.14).

Bytes for this operation are read from the contained input stream.

22.11.16 public final String readUTF() throws IOException

See the general contract of the readUTF method of DataInput (§22.1.15).

Bytes for this operation are read from the contained input stream.

22.11.17 public final static String readUTF(DataInput in)
throws IOException

The readUTF method reads from the stream in a representation of a Unicode character string encoded in Java modified UTF-8 format; this string of characters is then returned as a String. The details of the modified UTF-8 representation are exactly the same as for the readUTF method of DataInput (§22.1.15).

22.12 The Class java.io.LineNumberInputStream

A LineNumberInputStream adds functionality to another input stream, namely the ability to count lines. When the LineNumberInputStream is created, the line number counter is set to zero. As bytes from the stream are read or skipped, the counter is incremented whenever a line terminator (\n, \r, or \r\n) is encountered. Such line terminators are also converted to a single '\n' character. The method getLineNumber returns the current value of the counter, and the method setLineNumber sets the counter to a given integer value. If the contained input stream supports the mark operation, then so does the LineNumberInputStream; the mark operation remembers the line number counter and the reset operation sets the counter to the value remembered by the mark operation. 

public class LineNumberInputStream extends FilterInputStream {
	public LineNumberInputStream(InputStream in);
	public int read() throws IOException;
	public int read(byte[] b)
		throws IOException, NullPointerException;
	public int read(byte[] b, int off, int len)

		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public long skip(long n) throws IOException;
	public int available() throws IOException;
	public void mark(int readlimit);
	public void reset() throws IOException;
	public int getLineNumber();
	public void setLineNumber(int lineNumber);
}

22.12.1 public LineNumberInputStream(InputStream in)

This constructor initializes a newly created LineNumberInputStream by saving its argument, the input stream in, for later use.

22.12.2 public int read() throws IOException

See the general contract of the read method of InputStream (§22.3.1).

As bytes are read from the contained input stream, line terminators are recognized and counted. For each line terminator recognized in the contained input stream, a single character '\n' is returned.

Overrides the read method of FilterInputStream (§22.9.3).

22.12.3 public int read(byte[] b)
throws IOException, NullPointerException

See the general contract of the read method of InputStream (§22.3.2).

As bytes are read from the contained input stream, line terminators are recognized and counted. For each line terminator recognized in the contained input stream, a single character '\n' is returned.

Overrides the read method of FilterInputStream (§22.9.4).

22.12.4 public int read(byte[] b, int off, int len)
throws IOException, NullPointerException, IndexOutOfBoundsException

See the general contract of the read method of InputStream (§22.3.3).

As bytes are read from the contained input stream, line terminators are recognized and counted. For each line terminator recognized in the contained input stream, a single character '\n' is returned.

Overrides the read method of FilterInputStream (§22.9.5).

22.12.5 public long skip(long n) throws IOException

See the general contract of the skip method of InputStream (§22.3.4).

As bytes are read from the contained input stream, line terminators are recognized and counted. Each line terminator recognized in the contained input stream is considered to be a single byte skipped, even if it is the sequence \r\n.

Overrides the skip method of FilterInputStream (§22.9.6).

22.12.6 public int available() throws IOException

See the general contract of the available method of InputStream (§22.3.5).

Note that if the contained input stream is able to supply k input characters without blocking, the LineNumberInputStream can guarantee only to provide characters without blocking, because the k characters from the contained input stream might consist of \r\n pairs, which will be converted to just '\n' characters.

Overrides the available method of FilterInputStream (§22.9.7).

22.12.7 public void mark(int readlimit)

See the general contract of the mark method of InputStream (§22.3.7).

Marking a point in the input stream remembers the current line number as it would be returned by getLineNumber (§22.12.9).

Overrides the mark method of FilterInputStream (§22.9.9).

22.12.8 public void reset() throws IOException

See the general contract of the reset method of InputStream (§22.3.8).

Resetting the input stream to a previous point also resets the line number to the value it had at the marked point.

Overrides the reset method of FilterInputStream (§22.9.10).

22.12.9 public int getLineNumber()

The current line number is returned. This quantity depends on k, the number of line terminators encountered since the most recent occurrence of one of the following three kinds of events:

These rules imply that the current line number is 0 as the characters of the first line are read, and becomes 1 after the line terminator for the first line has been read.

22.12.10 public void setLineNumber(int lineNumber)

The current line number is set equal to the argument.

22.13 The Class java.io.PushbackInputStream

A PushbackInputStream adds functionality to another input stream, namely the ability to "push back" or "unread" one byte. This is useful in situations where it is convenient for a fragment of code to read an indefinite number of data bytes that are delimited by a particular byte value; after reading the terminating byte, the code fragment can "unread" it, so that the next read operation on the input stream will reread the byte that was pushed back. For example, bytes representing the characters constituting an identifier might be terminated by a byte representing an operator character; a method whose job is to read just an identifier can read until it sees the operator and then push the operator back to be re-read. 

public class PushbackInputStream extends FilterInputStream {
	protected int	 pushBack = -1;
	public PushbackInputStream(InputStream in);
	public int read() throws IOException;
	public int read(byte[] bytes, int offset, int length)
		throws IOException, NullPointerException,
			IndexOutOfBoundsException;
	public void unread(int ch) throws IOException;
	public int available() throws IOException;
	public boolean markSupported();
}

22.13.1 protected int pushBack = -1;

If this field has a nonnegative value, it is a byte that was pushed back. If this field is -1, there is currently no pushed-back byte.

22.13.2 public PushbackInputStream(InputStream in)

This constructor initializes a newly created PushbackInputStream by saving its argument, the input stream in, for later use. Initially, there is no pushed-back byte (the field pushBack is initialized to -1).

22.13.3 public int read() throws IOException

See the general contract of the read method of InputStream (§22.3.1).

If pushBack is not -1, the value of pushBack is returned and pushBack is set to -1. Otherwise, a byte is obtained from the contained input stream.

Overrides the read method of FilterInputStream (§22.9.3).

22.13.4 public int read(byte[] bytes, int offset, int length) throws IOException, NullPointerException, IndexOutOfBoundsException

See the general contract of the read method of InputStream (§22.3.3).

If pushBack is not -1, it is used as an input byte (and pushBack is set to -1) before any bytes are read from the contained input stream.

Overrides the read method of FilterInputStream (§22.9.5).

22.13.5 public void unread(int b) throws IOException

If pushBack is not -1, an IOException is thrown (it is not permitted to push back more than one byte). Otherwise, the byte value b is pushed back by assigning b to pushBack.

22.13.6 public int available() throws IOException

See the general contract of the available method of InputStream (§22.3.1).

This method first calls the available method of the contained input stream. If pushBack is -1, the result is returned; otherwise, the result plus 1 is returned.

Overrides the available method of FilterInputStream (§22.9.7).

22.13.7 public boolean markSupported()

This method returns false (a PushbackInputStream does not support mark).

22.14 The Class java.io.StreamTokenizer

A StreamTokenizer takes an input stream and parses it into "tokens," allowing the tokens to be read one at a time. The parsing process is controlled by a table and a number of flags that can be set to various states, allowing recognition of identifiers, numbers, quoted strings, and comments in a standard style. 

public class StreamTokenizer {
	public static final int TT_EOF = -1;
	public static final int TT_EOL = '\n';
	public static final int TT_NUMBER = -2;
	public static final int TT_WORD = -3;
	public int ttype;
	public String sval;
	public double nval;
	public StreamTokenizer(InputStream in);
	public void resetSyntax();
	public void wordChars(int low, int hi);
	public void whitespaceChars(int low, int hi);
	public void ordinaryChars(int low, int hi);
	public void ordinaryChar(int ch);
	public void commentChar(int ch);
	public void quoteChar(int ch);
	public void parseNumbers();
	public void eolIsSignificant(boolean flag);
	public void slashStarComments(boolean flag);
	public void slashSlashComments(boolean flag);
	public void lowerCaseMode(boolean flag);
	public int nextToken() throws IOException;
	public void pushBack();
	public int lineno();
	public String toString();
}
Each byte read from the input stream is regarded as a character in the range '\u0000' through '\u00FF'. The character value is used to look up five possible attributes of the character: whitespace, alphabetic, numeric, string quote, and comment character (a character may have more than one of these attributes, or none at all). In addition, there are three flags controlling whether line terminators are to be recognized as tokens, whether Java-style end-of-line comments that start with // should be recognized and skipped, and whether Java-style "traditional" comments delimited by /* and */ should be recognized and skipped. One more flag controls whether all the characters of identifiers are converted to lowercase.

Here is a simple example of the use of a StreamTokenizer. The following code merely reads all the tokens in the standard input stream and prints an identification of each one. Changes in the line number are also noted.

import java.io.StreamTokenizer;
import java.io.IOException;


class Tok {
	public static void main(String[] args) {
		StreamTokenizer st = new StreamTokenizer(System.in);
		st.ordinaryChar('/');
		int lineNum = -1;
		try {
			for (int tokenType = st.nextToken();
					tokenType != StreamTokenizer.TT_EOF;
					tokenType = st.nextToken()) {
				int newLineNum = st.lineno();
				if (newLineNum != lineNum) {
					System.out.println("[line " + newLineNum
											+ "]");
					lineNum = newLineNum;
				}
				switch(tokenType) {
				case StreamTokenizer.TT_NUMBER:
					System.out.println("the number " + st.nval);
					break;
				case StreamTokenizer.TT_WORD:
					System.out.println("identifier " + st.sval);
					break;
				default:
					System.out.println("  operator "
											+ (char)tokenType);
				}
			}
		} catch (IOException e) {
			System.out.println("I/O failure");
		}
	}
}
If the input stream contains this data: 


10 LET A = 4.5
20 LET B = A*A
30 PRINT A, B
then the resulting output is: 


[line 1]
the number 10.0
identifier LET
identifier A
  operator =
the number 4.5
[line 2]
the number 20.0
identifier LET
identifier B
  operator =
identifier A
  operator *
identifier A
[line 3]
the number 30.0
identifier PRINT
identifier A
  operator ,
identifier B

22.14.1 public static final int TT_EOF = -1;

A constant that indicates end of file was reached.

22.14.2 public static final int TT_EOL