graph2.java

程序练习中包括书中实例程序代码和练习中要用到的代码,是压缩文件

package examples.inner;

import java.util.Hashtable;
import java.util.Enumeration;

/** Class representing an undirected graph composed
  * of nodes.  The node class is a top-level class
  * nested within the Graph2 class.
  */
public class Graph2 {

   private Hashtable nodeList = new Hashtable();

   /** Add a node to the graph
     * @param x the x coordinate of the node
     * @param y the y coordinate of the node
     */
   public void addNode( int x, int y ) {
     // the use of "this." is not required here
     this.new Node( x, y );
   }

   /** Get the object as a string
     * @return the object as a string
     */
   public String toString() {
      StringBuffer sb = new StringBuffer( "[ " );
      Enumeration e = nodeList.elements();
      while ( e.hasMoreElements() ) {
         sb.append( e.nextElement().toString()
                    + " " );
      }
      sb.append( "]" );
      return sb.toString();
   }

   /** Test method
     * @param args not used
     */
   public static void main( String[] args ) {
      System.out.println( "creating the graph" );
      Graph2 g = new Graph2();
      System.out.println( "adding nodes" );
      g.addNode( 4, 5 );
      g.addNode( -6, 11 );
      System.out.println( g );
   }

   /** The class representing nodes within the graph
     */
   private class Node {

      private int x, y;

      public Node( int x, int y ) {
         this.x = x;
         this.y = y;
         // the use of "Graph2.this." is not
         // required here
         if ( ! Graph2.this.nodeList
                      .containsKey( key() ) ) {
            nodeList.put( key(), this );
         }
      }

      /** Determine the key value for a node
        * @return the key as a String
        */
      public Object key() {
         return x + "," + y;
      }

      /** Get the object as a string
        * @return the object as a string
        */
      public String toString() {
         return "(" + x + "," + y + ")";
      }
   } // end of Node class

} // end of Graph2 class