程序包 java.io

类 PushbackInputStream

java.lang.Object

java.io.InputStream

java.io.FilterInputStream

java.io.PushbackInputStream

所有已实现的接口:

Closeable, AutoCloseable

public class PushbackInputStream
extends FilterInputStream

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.

从以下版本开始:

JDK1.0

字段概要

字段

限定符和类型	字段	说明
protected byte[]	buf	The pushback buffer.
protected int	pos	The position within the pushback buffer from which the next byte will be read.

从类继承的字段 java.io.FilterInputStream

in

构造器概要

构造器

构造器	说明
PushbackInputStream(InputStream in)	Creates a PushbackInputStream and saves its argument, the input stream in, for later use.
PushbackInputStream(InputStream in, int size)	Creates a PushbackInputStream with a pushback buffer of the specified size, and saves its argument, the input stream in, for later use.

方法概要

限定符和类型	方法	说明
int	available()	Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.
void	close()	Closes this input stream and releases any system resources associated with the stream.
void	mark(int readlimit)	Marks the current position in this input stream.
boolean	markSupported()	Tests if this input stream supports the mark and reset methods, which it does not.
int	read()	Reads the next byte of data from this input stream.
int	read(byte[] b, int off, int len)	Reads up to len bytes of data from this input stream into an array of bytes.
void	reset()	Repositions this stream to the position at the time the mark method was last called on this input stream.
long	skip(long n)	Skips over and discards n bytes of data from this input stream.
void	unread(byte[] b)	Pushes back an array of bytes by copying it to the front of the pushback buffer.
void	unread(byte[] b, int off, int len)	Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer.
void	unread(int b)	Pushes back a byte by copying it to the front of the pushback buffer.

从类继承的方法 java.io.FilterInputStream

read

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

字段详细资料

buf

protected byte[] buf

The pushback buffer.

从以下版本开始:

JDK1.1

pos

protected int pos

The position within the pushback buffer from which the next byte will be read. When the buffer is empty, pos is equal to buf.length; when the buffer is full, pos is equal to zero.

从以下版本开始:

JDK1.1

构造器详细资料

PushbackInputStream

public PushbackInputStream(InputStream in,
                           int size)

Creates a PushbackInputStream with a pushback buffer of the specified size, and saves its argument, the input stream in, for later use. Initially, there is no pushed-back byte (the field pushBack is initialized to -1).

参数:

in - the input stream from which bytes will be read.

size - the size of the pushback buffer.

抛出:

IllegalArgumentException - if size <= 0

从以下版本开始:

JDK1.1

PushbackInputStream

public PushbackInputStream(InputStream in)

Creates a PushbackInputStream and saves its argument, the input stream in, for later use. Initially, there is no pushed-back byte (the field pushBack is initialized to -1).

参数:

in - the input stream from which bytes will be read.

方法详细资料

read

public int read()
         throws IOException

Reads the next byte of data from this input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

This method returns the most recently pushed-back byte, if there is one, and otherwise calls the read method of its underlying input stream and returns whatever value that method returns.

覆盖:

read 在类中 FilterInputStream

返回:

the next byte of data, or -1 if the end of the stream has been reached.

抛出:

IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.

另请参阅:

InputStream.read()

read

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

Reads up to len bytes of data from this input stream into an array of bytes. This method first reads any pushed-back bytes; after that, if fewer than len bytes have been read then it reads from the underlying input stream. If len is not zero, the method blocks until at least 1 byte of input is available; otherwise, no bytes are read and 0 is returned.

覆盖:

read 在类中 FilterInputStream

参数:

b - the buffer into which the data is read.

off - the start offset in the destination array b

len - the maximum number of bytes read.

返回:

the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

抛出:

NullPointerException - If b is null.

IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off

IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.

另请参阅:

InputStream.read(byte[], int, int)

unread

public void unread(int b)
            throws IOException

Pushes back a byte by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value (byte)b.

参数:

b - the int value whose low-order byte is to be pushed back.

抛出:

IOException - If there is not enough room in the pushback buffer for the byte, or this input stream has been closed by invoking its close() method.

unread

public void unread(byte[] b,
                   int off,
                   int len)
            throws IOException

Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value b[off], the byte after that will have the value b[off+1], and so forth.

参数:

b - the byte array to push back.

off - the start offset of the data.

len - the number of bytes to push back.

抛出:

IOException - If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking its close() method.

从以下版本开始:

JDK1.1

unread

public void unread(byte[] b)
            throws IOException

Pushes back an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value b[0], the byte after that will have the value b[1], and so forth.

参数:

b - the byte array to push back

抛出:

IOException - If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking its close() method.

从以下版本开始:

JDK1.1

available

public int available()
              throws IOException

Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

The method returns the sum of the number of bytes that have been pushed back and the value returned by available.

覆盖:

available 在类中 FilterInputStream

返回:

the number of bytes that can be read (or skipped over) from the input stream without blocking.

抛出:

IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.

另请参阅:

FilterInputStream.in, InputStream.available()

skip

public long skip(long n)
          throws IOException

Skips over and discards n bytes of data from this input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly zero. If n is negative, no bytes are skipped.

The skip method of PushbackInputStream first skips over the bytes in the pushback buffer, if any. It then calls the skip method of the underlying input stream if more bytes need to be skipped. The actual number of bytes skipped is returned.

覆盖:

skip 在类中 FilterInputStream

参数:

n - the number of bytes to be skipped.

返回:

the actual number of bytes skipped.

抛出:

IOException - if the stream does not support seek, or the stream has been closed by invoking its close() method, or an I/O error occurs.

从以下版本开始:

1.2

另请参阅:

FilterInputStream.in, InputStream.skip(long n)

markSupported

public boolean markSupported()

Tests if this input stream supports the mark and reset methods, which it does not.

覆盖:

markSupported 在类中 FilterInputStream

返回:

false, since this class does not support the mark and reset methods.

另请参阅:

InputStream.mark(int), InputStream.reset()

mark

public void mark(int readlimit)

Marks the current position in this input stream.

The mark method of PushbackInputStream does nothing.

覆盖:

mark 在类中 FilterInputStream

参数:

readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.

另请参阅:

InputStream.reset()

reset

public void reset()
           throws IOException

Repositions this stream to the position at the time the mark method was last called on this input stream.

The method reset for class PushbackInputStream does nothing except throw an IOException.

覆盖:

reset 在类中 FilterInputStream

抛出:

IOException - if this method is invoked.

另请参阅:

InputStream.mark(int), IOException

close

public void close()
           throws IOException

Closes this input stream and releases any system resources associated with the stream. Once the stream has been closed, further read(), unread(), available(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.

指定者:

close 在接口中 AutoCloseable

指定者:

close 在接口中 Closeable

覆盖:

close 在类中 FilterInputStream

抛出:

IOException - if an I/O error occurs.

另请参阅:

FilterInputStream.in