Java中Hashtable的应用之重载hashCode和equals

java中为了方便对以类为key的比较，需要重载作为key的类的hashCode和equals函数，以下为一简单实例:

import java.util.*;class GroundDog {// Identifier of the GroundDog.int ghNumber;GroundDog(int i) {ghNumber = i;}// Override hashCode.public int hashCode() {return ghNumber;}// Override equals.public boolean equals(Object o) {if ((o != null) && (o instanceof GroundDog))return ghNumber == ((GroundDog) o).ghNumber;elsereturn false;}}class Prediction {boolean shadow = Math.random() > 0.5;public String toString() {if (shadow)return "Six more weeks of winter";elsereturn "Early Spring!";}}public class HashtableDemo {public static void main(String[] args) {Hashtable ht = new Hashtable();for (int i = 0; i < 10; ++i) {ht.put(new GroundDog(i), new Prediction());}System.out.println("ht = " + ht + "/n");System.out.println("Looking up prediction for groundhog #3: ");GroundDog gh = new GroundDog(3);if (ht.containsKey(gh)) {System.out.println((Prediction) ht.get(gh));}}}