java中Comparable的例子和用法

Comparable的用法 
马克- to-win：马克 java社区：防盗版实名手机尾号： 73203。
马克-to-win：前面讲过进入TreeSet的每个元素是都排了序的，如果被添加的元素是我们自己定义的，就需要告诉TreeSet排序的规则，这个规则就要在Comparable中定义。在下面的例子中，当我们要往TreeSet中添加我们自己定义的类Worker对象时，就在compareTo中定义排序规则。



例：3.5.1
/*why in the past never implements Comparable? becasue Integer claas and
String class both implements this Comparable.
java.lang.Object
java.lang.String
All Implemented Interfaces:
CharSequence, Comparable, Serializable
 */

import java.util.*;
//Comparable接口在java.lang包中定义
//定义的方法：
//int compareTo(Object o);
//实现该接口就可以实现按用户定义的自然顺序排列对象。
/*you must implements Comparable,otherwise, when you add the second element into
 the treeset, it will report error, because it will search for Comparable
 interface. */
class Worker implements Comparable {
    int workNum;
    String name;
    int money;

    public Worker(int workNum, String name, int money) {
        this.workNum = workNum;
        this.name = name;
        this.money = money;
    }



    // 按工资排序
    /*
     * public int compareTo(Object o) Returns: a negative integer, zero, or a
     * positive integer as this object is less than, equal to, or greater than
     * the specified object. it looks like that the one that is in front is
     * small. what if two keys are the same? only print out one item.
     */
    public int compareTo(Object o) {
        Worker e = (Worker) o;
        return money - e.money;//到底谁减谁，讲师如想搞清楚，请听配套视频里的仔细分析。
        // return workNum - e.workNum;

    }

}




public class TestMark_to_win {
    public static void main(String[] args) {
        Worker e1 = new Worker(1, "李1", 5500);
        Worker e2 = new Worker(2, "李2", 6600);
        Worker e3 = new Worker(3, "李2", 4200);
        Worker e4 = new Worker(4, "李4", 2000);

        Collection c = new TreeSet();
       /* but a TreeSet instance performs all key comparisons using its
          compareTo (or compare) method, */
        c.add(e1);
        c.add(e2);
        c.add(e3);
        c.add(e4);

        Iterator i = c.iterator();
        while (i.hasNext()) {
            Worker e = (Worker) i.next();
            System.out.println(e.workNum + " " + e.name + " " + e.money);
        }
    }
}
结果：
4 李4 2000
3 李2 4200
1 李1 5500
2 李2 6600