Hashtable的hashCode的使用以及toString的复写——《Thinking in Java》随笔024

//: SpringDetector2.java
package cn.skyfffire;

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

/**
* @user: skyfffire
* @data: 2017年3月14日 
* @time: 下午6:31:13
*/
class Groundhog2 {
    int ghNumber;
    
    Groundhog2(int n) {
        ghNumber = n;
    }
    
    // Hashtable的get方法要使用这个方法
    @Override
    public int hashCode() {
        return ghNumber;
    }
    
    // HashTable的containsKey要使用
    @Override
    public boolean equals(Object o) {
        return (o instanceof Groundhog2) 
                && (ghNumber == ((Groundhog2)o).ghNumber);
    }
}

public class SpringDetector2 {
    public static void main(String[] args) {
        // 为了方便查看其中的键值对，复写了Hashtable的toString
        Hashtable<Groundhog2, Prediction> ht = 
                new Hashtable<Groundhog2, Prediction>() {
                    private static final long serialVersionUID = -8222553412985239408L;

                    @Override
                    public String toString() {
                        String str = "";
                        Enumeration<Groundhog2> ge = this.keys();
                        
                        while (ge.hasMoreElements()) {
                            Groundhog2 gh2 = ge.nextElement();
                            
                            str += (gh2 + " = " + this.get(gh2) + "
");
                        }
                        
                        return str;
                    }
        };
        
        // 添加十个键值对
        for (int i = 0; i < 10; i++) {
            ht.put(new Groundhog2(i), new Prediction());
        }
        
        // 查看键值对中的内容
        System.out.println(ht.toString());
        System.out.println(
                "Looking up prediction for groundhog #3:");
        
        // 复写了hashCode之后可以方便地比较ghNumber相同的键
        Groundhog2 hg = new Groundhog2(3);
        
        if (ht.containsKey(hg)) {
            System.out.println((Prediction)ht.get(hg));
        }
    }
}

///:~