PushbackInputStreampublic 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. |
| Fields Summary |
|---|
| protected byte[] | bufThe pushback buffer. | | protected int | posThe 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. |
| Constructors Summary |
|---|
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).
super(in);
if (size <= 0) {
throw new IllegalArgumentException("size <= 0");
}
this.buf = new byte[size];
this.pos = size;
| 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).
this(in, 1);
|
| Methods Summary |
|---|
| public 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. 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 {@link
java.io.FilterInputStream#available available}.
ensureOpen();
return (buf.length - pos) + super.available();
| | public synchronized void | close()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.
if (in == null)
return;
in.close();
in = null;
buf = null;
| | private void | ensureOpen()Check to make sure that this stream has not been closed
if (in == null)
throw new IOException("Stream closed");
| | public synchronized void | mark(int readlimit)Marks the current position in this input stream.
The mark method of PushbackInputStream
does nothing.
| | public boolean | markSupported()Tests if this input stream supports the mark and
reset methods, which it does not.
return false;
| | public int | read()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.
ensureOpen();
if (pos < buf.length) {
return buf[pos++] & 0xff;
}
return super.read();
| | public int | read(byte[] b, int off, int len)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.
ensureOpen();
if (b == null) {
throw new NullPointerException();
} else if (off < 0 || len < 0 || len > b.length - off) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
int avail = buf.length - pos;
if (avail > 0) {
if (len < avail) {
avail = len;
}
System.arraycopy(buf, pos, b, off, avail);
pos += avail;
off += avail;
len -= avail;
}
if (len > 0) {
len = super.read(b, off, len);
if (len == -1) {
return avail == 0 ? -1 : avail;
}
return avail + len;
}
return avail;
| | public synchronized void | reset()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.
throw new IOException("mark/reset not supported");
| | public long | skip(long n)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.
ensureOpen();
if (n <= 0) {
return 0;
}
long pskip = buf.length - pos;
if (pskip > 0) {
if (n < pskip) {
pskip = n;
}
pos += pskip;
n -= pskip;
}
if (n > 0) {
pskip += super.skip(n);
}
return pskip;
| | public void | unread(int b)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.
ensureOpen();
if (pos == 0) {
throw new IOException("Push back buffer is full");
}
buf[--pos] = (byte)b;
| | public 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. 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.
ensureOpen();
if (len > pos) {
throw new IOException("Push back buffer is full");
}
pos -= len;
System.arraycopy(b, off, buf, pos, len);
| | public void | unread(byte[] b)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.
unread(b, 0, b.length);
|
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