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 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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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 java.io.BufferedInputStream
 * @see java.io.ByteArrayInputStream
 * @see java.io.DataInputStream
 * @see java.io.FilterInputStream
 * @see java.io.InputStream#read()
 * @see java.io.OutputStream
 * @see java.io.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 java.io.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 java.io.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 java.io.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 java.io.InputStream#mark(int)
 * @see java.io.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 java.io.InputStream#mark(int)
 * @see java.io.InputStream#reset()
 */
 public boolean markSupported() {
 return false;
 }

}