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.
 *
 * @see java.io.ByteArrayInputStream
 * @see java.io.DataInputStream
 * @see java.io.FilterInputStream
 * @see java.io.InputStream#read()
 * @see java.io.OutputStream
 */
public abstract class InputStream implements Closeable {

    /**
     * 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 {
        throw new RuntimeException();
    }

    /**
     * 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 {
        throw new RuntimeException();
    }

    /**
     * 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 void mark(int readlimit) {
        throw new RuntimeException();
    }

    /**
     * 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() {
        throw new RuntimeException();
    }

    /**
     * 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 {
        throw new RuntimeException();
    }

    /**
     * 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 {
        throw new RuntimeException();
    }

    /**
     * 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 void reset() throws IOException {
        throw new RuntimeException();
    }

    /**
     * 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</code> is negative, no bytes are skipped.
     *
     * <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 {
        throw new RuntimeException();
    }
}