java.lang.Object java.io.InputStream
public abstract class InputStream
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.
Constructor Summary | |
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InputStream
() |
Method Summary | |
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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 |
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. |
abstract int |
read
() Reads the next byte of data from the input stream. |
int |
read
(byte[] b) Reads some number of bytes from the input stream and stores them into the buffer array b. |
int |
read
(byte[] b, int off, int len) Reads up to len bytes of data from the 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. |
Methods inherited from class java.lang. Object |
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clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
Constructor Detail |
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public InputStream()
Method Detail |
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public abstract int read() throws IOException
A subclass must provide an implementation of this method.
public int read(byte[] b) throws IOException
If b is null, a NullPointerException 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.
If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException 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)
public int read(byte[] b, int off, int len) throws IOException
This method blocks until input data is available, end of file is detected, or an exception is thrown.
If b is null, a NullPointerException is thrown.
If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException 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.
If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed.
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. Subclasses are encouraged to provide a more efficient implementation of this method.
public long skip(long n) throws IOException
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.
public int available() throws IOException
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.
public void close() throws IOException
The close method of InputStream does nothing.
public void mark(int readlimit)
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.
The mark method of InputStream does nothing.
public void reset() throws IOException
The general contract of reset is:
The method reset for class InputStream does nothing except throw an IOException.
public boolean markSupported()