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   * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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  package java.io;
  
  /**
   * This abstract class is the superclass of all classes representing
   * an input stream of bytes.
   *
   * <p> Applications that need to define a subclass of <code>InputStream</code>
   * must always provide a method that returns the next byte of input.
   *
   * @author  Arthur van Hoff
   * @see     BufferedInputStream
   * @see     ByteArrayInputStream
   * @see     DataInputStream
   * @see     FilterInputStream
   * @see     InputStream#read()
   * @see     OutputStream
   * @see     PushbackInputStream
   * @since   JDK1.0
   */
  public abstract class InputStream implements Closeable {
  
      // MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to
      // use when skipping.
      private static final int MAX_SKIP_BUFFER_SIZE = 2048;
  
      /**
       * Reads the next byte of data from the input stream. The value byte is
       * returned as an <code>int</code> in the range <code>0</code> to
       * <code>255</code>. If no byte is available because the end of the stream
       * has been reached, the value <code>-1</code> is returned. This method
       * blocks until input data is available, the end of the stream is detected,
       * or an exception is thrown.
       *
       * <p> A subclass must provide an implementation of this method.
       *
       * @return     the next byte of data, or <code>-1</code> if the end of the
       *             stream is reached.
       * @exception  IOException  if an I/O error occurs.
       */
      public abstract int read() throws IOException;
  
      /**
       * Reads some number of bytes from the input stream and stores them into
       * the buffer array <code>b</code>. 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.
       *
       * <p> If the length of <code>b</code> is zero, then no bytes are read and
       * <code>0</code> 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 <code>-1</code> is returned; otherwise, at
       * least one byte is read and stored into <code>b</code>.
       *
       * <p> The first byte read is stored into element <code>b[0]</code>, the
       * next one into <code>b[1]</code>, and so on. The number of bytes read is,
       * at most, equal to the length of <code>b</code>. Let <i>k</i> be the
       * number of bytes actually read; these bytes will be stored in elements
       * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
       * leaving elements <code>b[</code><i>k</i><code>]</code> through
       * <code>b[b.length-1]</code> unaffected.
       *
       * <p> The <code>read(b)</code> method for class <code>InputStream</code>
       * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
       *
       * @param      b   the buffer into which the data is read.
       * @return     the total number of bytes read into the buffer, or
       *             <code>-1</code> if there is no more data because the end of
       *             the stream has been reached.
       * @exception  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.
       * @exception  NullPointerException  if <code>b</code> is <code>null</code>.
       * @see        InputStream#read(byte[], int, int)
       */
      public int read(byte b[]) throws IOException {
          return read(b, 0, b.length);
      }
  
      /**
       * Reads up to <code>len</code> bytes of data from the input stream into
       * an array of bytes.  An attempt is made to read as many as
       * <code>len</code> bytes, but a smaller number may be read.
       * The number of bytes actually read is returned as an integer.
       *
       * <p> This method blocks until input data is available, end of file is
       * detected, or an exception is thrown.
       *
       * <p> If <code>len</code> is zero, then no bytes are read and
       * <code>0</code> 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 <code>-1</code> is returned; otherwise, at least one
       * byte is read and stored into <code>b</code>.
       *
       * <p> The first byte read is stored into element <code>b[off]</code>, the
       * next one into <code>b[off+1]</code>, and so on. The number of bytes read
       * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
       * bytes actually read; these bytes will be stored in elements
       * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
       * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
       * <code>b[off+len-1]</code> unaffected.
       *
       * <p> In every case, elements <code>b[0]</code> through
       * <code>b[off]</code> and elements <code>b[off+len]</code> through
       * <code>b[b.length-1]</code> are unaffected.
       *
       * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
       * for class <code>InputStream</code> simply calls the method
       * <code>read()</code> repeatedly. If the first such call results in an
       * <code>IOException</code>, that exception is returned from the call to
       * the <code>read(b,</code> <code>off,</code> <code>len)</code> method.  If
       * any subsequent call to <code>read()</code> results in a
       * <code>IOException</code>, the exception is caught and treated as if it
       * were end of file; the bytes read up to that point are stored into
       * <code>b</code> 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 <code>len</code> 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.
       *
       * @param      b     the buffer into which the data is read.
       * @param      off   the start offset in array <code>b</code>
       *                   at which the data is written.
       * @param      len   the maximum number of bytes to read.
       * @return     the total number of bytes read into the buffer, or
       *             <code>-1</code> if there is no more data because the end of
       *             the stream has been reached.
       * @exception  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.
       * @exception  NullPointerException If <code>b</code> is <code>null</code>.
       * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
       * <code>len</code> is negative, or <code>len</code> is greater than
       * <code>b.length - off</code>
       * @see        InputStream#read()
       */
      public int read(byte b[], int off, int len) throws IOException {
          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 c = read();
          if (c == -1) {
              return -1;
          }
          b[off] = (byte)c;
  
          int i = 1;
          try {
              for (; i < len ; i++) {
                  c = read();
                  if (c == -1) {
                      break;
                  }
                  b[off + i] = (byte)c;
              }
          } catch (IOException ee) {
          }
          return i;
      }
  
      /**
       * Skips over and discards <code>n</code> bytes of data from this input
       * stream. The <code>skip</code> method may, for a variety of reasons, end
       * up skipping over some smaller number of bytes, possibly <code>0</code>.
       * This may result from any of a number of conditions; reaching end of file
       * before <code>n</code> bytes have been skipped is only one possibility.
       * The actual number of bytes skipped is returned. If {@code n} is
       * negative, the {@code skip} method for class {@code InputStream} always
       * returns 0, and no bytes are skipped. Subclasses may handle the negative
       * value differently.
       *
       * <p> The <code>skip</code> method of this class creates a
       * byte array and then repeatedly reads into it until <code>n</code> 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.
       *
       * @param      n   the number of bytes to be skipped.
       * @return     the actual number of bytes skipped.
       * @exception  IOException  if the stream does not support seek,
       *                          or if some other I/O error occurs.
       */
      public long skip(long n) throws IOException {
  
          long remaining = n;
          int nr;
  
          if (n <= 0) {
              return 0;
          }
  
          int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
          byte[] skipBuffer = new byte[size];
          while (remaining > 0) {
              nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
              if (nr < 0) {
                  break;
              }
              remaining -= nr;
          }
  
          return n - remaining;
      }
  
      /**
       * 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.
       *
       * <p> Note that while some implementations of {@code 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.
       *
       * <p> A subclass' implementation of this method may choose to throw an
       * {@link IOException} if this input stream has been closed by
       * invoking the {@link #close()} method.
       *
       * <p> The {@code available} method for class {@code InputStream} always
       * returns {@code 0}.
       *
       * <p> This method should be overridden by subclasses.
       *
       * @return     an estimate of the number of bytes that can be read (or skipped
       *             over) from this input stream without blocking or {@code 0} when
       *             it reaches the end of the input stream.
       * @exception  IOException if an I/O error occurs.
       */
      public int available() throws IOException {
          return 0;
      }
  
      /**
       * Closes this input stream and releases any system resources associated
       * with the stream.
       *
       * <p> The <code>close</code> method of <code>InputStream</code> does
       * nothing.
       *
       * @exception  IOException  if an I/O error occurs.
       */
      public void close() throws IOException {}
  
      /**
       * Marks the current position in this input stream. A subsequent call to
       * the <code>reset</code> method repositions this stream at the last marked
       * position so that subsequent reads re-read the same bytes.
       *
       * <p> The <code>readlimit</code> arguments tells this input stream to
       * allow that many bytes to be read before the mark position gets
       * invalidated.
       *
       * <p> The general contract of <code>mark</code> is that, if the method
       * <code>markSupported</code> returns <code>true</code>, the stream somehow
       * remembers all the bytes read after the call to <code>mark</code> and
       * stands ready to supply those same bytes again if and whenever the method
       * <code>reset</code> is called.  However, the stream is not required to
       * remember any data at all if more than <code>readlimit</code> bytes are
       * read from the stream before <code>reset</code> is called.
       *
       * <p> Marking a closed stream should not have any effect on the stream.
       *
       * <p> The <code>mark</code> method of <code>InputStream</code> does
       * nothing.
       *
       * @param   readlimit   the maximum limit of bytes that can be read before
       *                      the mark position becomes invalid.
       * @see     InputStream#reset()
       */
      public synchronized void mark(int readlimit) {}
  
      /**
       * Repositions this stream to the position at the time the
       * <code>mark</code> method was last called on this input stream.
       *
       * <p> The general contract of <code>reset</code> is:
       *
       * <ul>
       * <li> If the method <code>markSupported</code> returns
       * <code>true</code>, then:
       *
       *     <ul><li> If the method <code>mark</code> has not been called since
       *     the stream was created, or the number of bytes read from the stream
       *     since <code>mark</code> was last called is larger than the argument
       *     to <code>mark</code> at that last call, then an
       *     <code>IOException</code> might be thrown.
       *
       *     <li> If such an <code>IOException</code> is not thrown, then the
       *     stream is reset to a state such that all the bytes read since the
       *     most recent call to <code>mark</code> (or since the start of the
       *     file, if <code>mark</code> has not been called) will be resupplied
       *     to subsequent callers of the <code>read</code> method, followed by
       *     any bytes that otherwise would have been the next input data as of
       *     the time of the call to <code>reset</code>. </ul>
       *
       * <li> If the method <code>markSupported</code> returns
       * <code>false</code>, then:
       *
       *     <ul><li> The call to <code>reset</code> may throw an
       *     <code>IOException</code>.
       *
       *     <li> If an <code>IOException</code> 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 <code>read</code> method depend on the
       *     particular type of the input stream. </ul></ul>
       *
       * <p>The method <code>reset</code> for class <code>InputStream</code>
       * does nothing except throw an <code>IOException</code>.
       *
       * @exception  IOException  if this stream has not been marked or if the
       *               mark has been invalidated.
       * @see     InputStream#mark(int)
       * @see     IOException
       */
      public synchronized void reset() throws IOException {
          throw new IOException("mark/reset not supported");
      }
  
      /**
       * Tests if this input stream supports the <code>mark</code> and
       * <code>reset</code> methods. Whether or not <code>mark</code> and
       * <code>reset</code> are supported is an invariant property of a
       * particular input stream instance. The <code>markSupported</code> method
       * of <code>InputStream</code> returns <code>false</code>.
       *
       * @return  <code>true</code> if this stream instance supports the mark
       *          and reset methods; <code>false</code> otherwise.
       * @see     InputStream#mark(int)
       * @see     InputStream#reset()
       */
      public boolean markSupported() {
          return false;
      }
  
  }
  