gcc/libjava/java/nio/channels/FileLock.java

/* FileLock.java --
   Copyright (C) 2002, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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exception statement from your version. */

package java.nio.channels;

import java.io.IOException;


/**
 * @since 1.4
 */
public abstract class FileLock
{
  FileChannel channel;
  long position;
  long size;
  boolean shared;

  /**
   * Initializes the file lock.
   *
   * @exception IllegalArgumentException If the preconditions on the parameters do not hold
   */
  protected FileLock(FileChannel channel, long position, long size,
                     boolean shared)
  {
    if (position < 0 || size < 0)
      throw new IllegalArgumentException();

    this.channel = channel;
    this.position = position;
    this.size = size;
    this.shared = shared;
  }

  /**
   * Tells whether or not this lock is valid.
   */
  public abstract boolean isValid();

  /**
   * Releases this lock.
   *
   * @exception IOException If an error occurs
   * @exception ClosedChannelException If the locked channel is no longer open.
   */
  public abstract void release() throws IOException;

  /**
   * Returns the file channel upon whose file this lock is held.
   */
  public final FileChannel channel()
  {
    return channel;
  }

  /**
   * Tells whether this lock is shared.
   */
  public final boolean isShared()
  {
    return shared;
  }

  /**
   * Tells whether or not this lock overlaps the given lock range.
   */
  public final boolean overlaps(long position, long size)
  {
    if (position > this.position + this.size)
      return false;

    if (position + size < this.position)
      return false;

    return true;
  }

  /**
   * Returns the position within the file of the first byte of the
   * locked region.
   */
  public final long position()
  {
    return position;
  }

  /**
   * Returns the size of the locked region in bytes.
   */
  public final long size()
  {
    return size;
  }

  /**
   * Returns a string describing the range, type, and validity of this lock.
   */
  public final String toString()
  {
    StringBuffer buf = new StringBuffer(getClass().getName());
    buf.append("[");
    buf.append(position);
    buf.append(":");
    buf.append(size);
    if (shared)
      buf.append(" shared");
    else
      buf.append(" exclusive");
    if (isValid())
      buf.append(" valid]");
    else
      buf.append(" invalid]");
    return buf.toString();
  }
}