public abstract class InputStream extends Object implements Closeable
This abstract class is the superclass of all classes representing an input stream of bytes.
Applications that need to define a subclass of InputStream
must always provide a method that returns the next byte of input.
BufferedInputStream
, ByteArrayInputStream
, DataInputStream
, FilterInputStream
, read()
, OutputStream
, PushbackInputStream
public InputStream()
public abstract int read() throws IOException
Reads the next byte of data from the 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.
A subclass must provide an implementation of this method.
-1
if the end of the stream is reached.IOException
- if an I/O error occurs.public int read(byte[] b) throws IOException
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 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 the end of the 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.
The read(b)
method for class InputStream
has the same effect as:
read(b, 0, b.length)
b
- the buffer into which the data is read.-1
if there is no more data because the end of the stream has been reached.IOException
- If the first byte cannot be read for any reason other than the end of the file, if the input stream has been closed, or if some other I/O error occurs.NullPointerException
- if b
is null
.read(byte[], int, int)
public int read(byte[] b, int off, int len) throws IOException
Reads up to len
bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len
bytes, but a smaller number may be read. 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 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.
The read(b,
off,
len)
method for class InputStream
simply 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. The default implementation of this method blocks until the requested amount of input data len
has been read, end of file is detected, or an exception is thrown. Subclasses are encouraged to provide a more efficient implementation of this method.
b
- the buffer into which the data is read.off
- the start offset in array b
at which the data is written.len
- the maximum number of bytes to read.-1
if there is no more data because the end of the stream has been reached.IOException
- If the first byte cannot be read for any reason other than end of file, or if the input stream has been closed, or if some other I/O error occurs.NullPointerException
- If b
is null
.IndexOutOfBoundsException
- If off
is negative, len
is negative, or len
is greater than b.length - off
read()
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 0
. 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. If n
is negative, the skip
method for class InputStream
always returns 0, and no bytes are skipped. Subclasses may handle the negative value differently.
The skip
method of this class creates a byte array and then repeatedly reads into it until n
bytes have been read or the end of the stream has been reached. Subclasses are encouraged to provide a more efficient implementation of this method. For instance, the implementation may depend on the ability to seek.
n
- the number of bytes to be skipped.IOException
- if the stream does not support seek, or if some other I/O error occurs.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.
Note that while some implementations of InputStream
will return the total number of bytes in the stream, many will not. It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream.
A subclass' implementation of this method may choose to throw an IOException
if this input stream has been closed by invoking the close()
method.
The available
method for class InputStream
always returns 0
.
This method should be overridden by subclasses.
0
when it reaches the end of the input stream.IOException
- if an I/O error occurs.public void close() throws IOException
Closes this input stream and releases any system resources associated with the stream.
The close
method of InputStream
does nothing.
close
in interface Closeable
close
in interface AutoCloseable
IOException
- if an I/O error occurs.public void mark(int readlimit)
Marks the current position in this input stream. A subsequent call to the reset
method repositions this stream at the last marked position so that subsequent reads re-read the same bytes.
The readlimit
arguments tells this input stream to allow that many bytes to be read before the mark position gets invalidated.
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.
Marking a closed stream should not have any effect on the stream.
The mark
method of InputStream
does nothing.
readlimit
- the maximum limit of bytes that can be read before the mark position becomes invalid.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 general contract of reset
is:
markSupported
returns true
, then: mark
has not been called since the stream was created, or the number of bytes read from the stream since mark
was last called is larger than the argument to mark
at that last call, then an IOException
might be thrown. IOException
is not thrown, then the stream is reset to a state such that all the bytes read since the most recent call to mark
(or since the start of the file, if mark
has not been called) will be resupplied to subsequent callers of the read
method, followed by any bytes that otherwise would have been the next input data as of the time of the call to reset
. markSupported
returns false
, then: reset
may throw an IOException
. IOException
is not thrown, then the stream is reset to a fixed state that depends on the particular type of the input stream and how it was created. The bytes that will be supplied to subsequent callers of the read
method depend on the particular type of the input stream. The method reset
for class InputStream
does nothing except throw an IOException
.
IOException
- if this stream has not been marked or if the mark has been invalidated.mark(int)
, IOException
public boolean markSupported()
Tests if this input stream supports the mark
and reset
methods. Whether or not mark
and reset
are supported is an invariant property of a particular input stream instance. The markSupported
method of InputStream
returns false
.
true
if this stream instance supports the mark and reset methods; false
otherwise.mark(int)
, reset()
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Documentation extracted from Debian's OpenJDK Development Kit package.
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