nodehandle.java

pastry的java实现的2.0b版

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"FreePastry" Peer-to-Peer Application Development Substrate 

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package rice.p2p.commonapi;

import java.io.*;
import java.util.*;

import rice.p2p.commonapi.rawserialization.OutputBuffer;

/**
 * @(#) NodeHandle.java This class is an abstraction of a node handle from the
 * CommonAPI paper. A node handle is a handle to a known node, which
 * conceptually includes the node's Id, as well as the node's underlying network
 * address (such as IP/port). This class is (unfortunately) an abstact class due
 * to the need to be observable.
 *
 * @version $Id: NodeHandle.java 3274 2006-05-15 16:17:47Z jeffh $
 * @author Alan Mislove
 * @author Peter Druschel
 */
public abstract class NodeHandle extends Observable implements Serializable {

  // constants defining types of observable events
  /**
   * DESCRIBE THE FIELD
   */
  public final static Integer PROXIMITY_CHANGED = new Integer(1);
  /**
   * DESCRIBE THE FIELD
   */
  public final static Integer DECLARED_DEAD = new Integer(2);
  /**
   * DESCRIBE THE FIELD
   */
  public final static Integer DECLARED_LIVE = new Integer(3);

  // serialver
  private final static long serialVersionUID = 4761193998848368227L;

  /**
   * Returns this node's id.
   *
   * @return The corresponding node's id.
   */
  public abstract Id getId();

  /**
   * Returns whether or not this node is currently alive
   *
   * @return Whether or not this node is currently alive
   */
  public abstract boolean isAlive();

  /**
   * Returns the current proximity value of this node
   *
   * @return The current proximity value of this node
   */
  public abstract int proximity();

  /**
   * Requests that the underlying transport layer check to ensure that the
   * remote node is live. If the node is found to be live, nothing happens, but
   * if the node does not respond, the transport layer make take steps to
   * verfify that the node is dead. Such steps could include finding an
   * alteranate route to the node.
   *
   * @return Whether or not the node is currently alive
   */
  public abstract boolean checkLiveness();

  /**
   * DESCRIBE THE METHOD
   *
   * @param buf DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public abstract void serialize(OutputBuffer buf) throws IOException;

}