# Class InputStream

java.lang.Object
java.io.InputStream

All Implemented Interfaces:
  `AutoCloseable`

Direct Known Subclasses:
  `BufferedInputStream, FilterInputStream`

public abstract class InputStream extends Object implements AutoCloseable
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, CLDC 1.0 See Also:ByteArrayInputStream, DataInputStream, read(), OutputStream

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `InputStream()`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `int`
  `available()`
  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.
  `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 Object

  `clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Constructor Details

  - ### InputStream

    public InputStream()

- ## Method Details

  - ### available

    public int available() throws java.io.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.
    Throws:
      `java.io.IOException`

  - ### close

    public void close() throws java.io.IOException
    Closes this input stream and releases any system resources associated with the stream. The close method of InputStream does nothing.
    Specified by:
      `close` in interface `AutoCloseable`
    Throws:
      `java.io.IOException`

  - ### 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 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.

  - ### markSupported

    public boolean markSupported()
    Tests if this input stream supports the mark and reset methods. The markSupported method of InputStream returns false.

  - ### read

    public abstract int read() throws java.io.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.
    Throws:
      `java.io.IOException`

  - ### read

    public int read(byte[] b) throws java.io.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, 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 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 elements b[0] through b[k-1], leaving elements b

    invalid reference

        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)

    Throws:
      `java.io.IOException`

  - ### read

    public int read(byte[] b, int off, int len) throws java.io.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, possibly zero. 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, 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

    invalid reference

        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
    invalid reference

        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

    invalid reference

        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.

    Throws:
      `java.io.IOException`

  - ### reset

    public void reset() throws java.io.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: If the method markSupported returns true, 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 an IOException 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 returns false, then: The call to reset may throw an IOException. 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 and always throws an IOException.
    Throws:
      `java.io.IOException`

  - ### skip

    public long skip(long n) throws java.io.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.
    Throws:
      `java.io.IOException`