java.lang.Object
- java.io.InputStream
- - java.io.FilterInputStream
  - - java.io.PushbackInputStream

All Implemented Interfaces:

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.

Since:

JDK1.0

Field Summary
Fields
Modifier and Type Field and Description

protected byte[] buf
The pushback buffer.

protected int pos
The position within the pushback buffer from which the next byte will be read.

PushbackInputStream (Java Platform SE 7 ) Home of API Java Contents Haut
- Fields inherited from class java.io.FilterInputStream in

Constructor Summary

Constructors
Constructor and Description
`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.

PushbackInputStream (Java Platform SE 7 ) Home of API Java Contents Haut

Method Summary

Methods
Modifier and Type	Method and Description
`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.

PushbackInputStream (Java Platform SE 7 ) Home of API Java Contents Haut

Methods inherited from class java.io.FilterInputStream read

Methods inherited from class java.lang.Object clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - buf
    protected byte[] buf
    
    The pushback buffer.
    
    Since:
    
    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.
    
    Since:
    
    JDK1.1
- Constructor Detail
  - 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).
    
    Parameters:
    in - the input stream from which bytes will be read.
    size - the size of the pushback buffer.
    
    Throws:
    
    IllegalArgumentException - if size is <= 0
    Since:
    
    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).
    
    Parameters:
    in - the input stream from which bytes will be read.
- Method Detail
  - 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.
    
    Overrides:
    
    read in class FilterInputStream
    
    Returns:
    the next byte of data, or -1 if the end of the stream has been reached.
    
    Throws:
    
    IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.
    See Also:
    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.
    
    Overrides:
    
    read in class FilterInputStream
    
    Parameters:
    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.
    
    Returns:
    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.
    
    Throws:
    
    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.
    See Also:
    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.
    
    Parameters:
    b - the int value whose low-order byte is to be pushed back.
    
    Throws:
    
    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.
    
    Parameters:
    b - the byte array to push back.
    off - the start offset of the data.
    len - the number of bytes to push back.
    
    Throws:
    
    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.
    Since:
    
    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.
    
    Parameters:
    b - the byte array to push back
    
    Throws:
    
    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.
    Since:
    
    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.
    
    Overrides:
    
    available in class FilterInputStream
    
    Returns:
    the number of bytes that can be read (or skipped over) from the input stream without blocking.
    
    Throws:
    
    IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.
    See Also:
    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.
    
    Overrides:
    
    skip in class FilterInputStream
    
    Parameters:
    n - the number of bytes to be skipped.
    
    Returns:
    the actual number of bytes skipped.
    
    Throws:
    
    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.
    Since:
    
    1.2
    
    See Also:
    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.
    
    Overrides:
    
    markSupported in class FilterInputStream
    
    Returns:
    false, since this class does not support the mark and reset methods.
    See Also:
    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.
    
    Overrides:
    
    mark in class FilterInputStream
    
    Parameters:
    readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.
    See Also:
    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.
    
    Overrides:
    
    reset in class FilterInputStream
    
    Throws:
    
    IOException - if this method is invoked.
    See Also:
    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.
    
    Specified by:
    
    close in interface Closeable
    
    Specified by:
    
    close in interface AutoCloseable
    
    Overrides:
    
    close in class FilterInputStream
    
    Throws:
    
    IOException - if an I/O error occurs.
    See Also:
    FilterInputStream.in

Document created the 11/06/2005, last modified the 04/03/2020
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References

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Contents Haut

Modifier and Type	Field and Description
`protected byte[]`	`buf` The pushback buffer.
`protected int`	`pos` The position within the pushback buffer from which the next byte will be read.

Class PushbackInputStream

References