3.5 Comparable的用法  

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;     } } 更多请见：https://blog.csdn.net/qq_43650923/article/details/100831985