InputStream (Java 2 Platform SE 5.0) (original) (raw)

java.io

Class InputStream

java.lang.Object java.io.InputStream

All Implemented Interfaces:

Closeable

Direct Known Subclasses:

AudioInputStream, ByteArrayInputStream, FileInputStream, FilterInputStream, InputStream, ObjectInputStream, PipedInputStream, SequenceInputStream, StringBufferInputStream

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.

Since:

JDK1.0

See Also:

BufferedInputStream, ByteArrayInputStream, DataInputStream, FilterInputStream, read(), OutputStream, PushbackInputStream

InputStream

public InputStream()

read

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 to255. 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.

Returns:

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

Throws:

[IOException](../../java/io/IOException.html "class in java.io") - if an I/O error occurs.

read

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 b is null, aNullPointerException is thrown. If the length ofb 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 elementsb[0] through b[k-1], leaving elements b[k] throughb[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, anIOException is thrown if the input stream has been closed.

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

 read(b, 0, b.length) 

Parameters:

b - the buffer into which the data is read.

Returns:

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

Throws:

[IOException](../../java/io/IOException.html "class in java.io") - if an I/O error occurs.

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if b is null.

See Also:

[read(byte[], int, int)](../../java/io/InputStream.html#read%28byte[], int, int%29)

read

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 aslen 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 b is null, aNullPointerException is thrown.

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

If len is zero, then no bytes are read and0 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 elementsb[off] through b[off+k-1], leaving elements b[off+k] throughb[off+len-1] unaffected.

In every case, elements b[0] throughb[off] and elements b[off+len] throughb[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, anIOException is thrown if the input stream has been closed.

The read(b, off, len) method for class InputStream simply calls the methodread() repeatedly. If the first such call results in anIOException, that exception is returned from the call to the read(b, off, len) method. If any subsequent call to read() results in aIOException, the exception is caught and treated as if it were end of file; the bytes read up to that point are stored intob and the number of bytes read before the exception occurred is returned. Subclasses are encouraged to provide a more efficient implementation of this method.

Parameters:

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.

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:

[IOException](../../java/io/IOException.html "class in java.io") - if an I/O error occurs.

[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang") - if b is null.

See Also:

read()

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 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, no bytes are skipped.

The skip method of InputStream 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.

Parameters:

n - the number of bytes to be skipped.

Returns:

the actual number of bytes skipped.

Throws:

[IOException](../../java/io/IOException.html "class in java.io") - if an I/O error occurs.

available

public int available() throws IOException

Returns the number of bytes that can be read (or skipped over) from this input stream without blocking by the next caller of a method for this input stream. The next caller might be the same thread or another thread.

The available method for class InputStream always returns 0.

This method should be overridden by subclasses.

Returns:

the number of bytes that can be read from this input stream without blocking.

Throws:

[IOException](../../java/io/IOException.html "class in java.io") - if an I/O error occurs.

close

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.

Specified by:

[close](../../java/io/Closeable.html#close%28%29) in interface [Closeable](../../java/io/Closeable.html "interface in java.io")

Throws:

[IOException](../../java/io/IOException.html "class in java.io") - if an I/O error occurs.

mark

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 methodmarkSupported 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 methodreset 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 of InputStream does nothing.

Parameters:

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

See Also:

reset()

reset

public void reset() throws IOException

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

The general contract of reset is:

• If the method markSupported returnstrue, then:
  • If the method 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 anIOException might be thrown.
  • If such an 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.
• If the method markSupported returnsfalse, then:
  • The call to reset may throw anIOException.
  • If an 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.

Throws:

[IOException](../../java/io/IOException.html "class in java.io") - if this stream has not been marked or if the mark has been invalidated.

See Also:

mark(int), IOException

markSupported

public boolean markSupported()

Tests if this input stream supports the mark andreset methods. Whether or not mark andreset are supported is an invariant property of a particular input stream instance. The markSupported method of InputStream returns false.

Returns:

true if this stream instance supports the mark and reset methods; false otherwise.

See Also:

mark(int), reset()

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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