TreeSet集合內部排序

import java.util.*;

/*
    TreeSet集合內部實現了排序

    1. 自定義對象需要實現Comparable接口的compareTo方法，自定義排序規則,return 1（第一個元素大於第二個元素），0（相等），-1（小於） 
【正數負數均可，不一定要是1或者-1】

    2. 如果元素本身的排序規則不適用，那麼自定義比較器實現Comparator接口，並在初始化集合的時傳入。

    3. 底層數據結構是二叉樹，大於放右邊，小於放左邊
*/

class TreeSetDemo {
    public static void main(String[] args) {
        TreeSet ts = new TreeSet(new Mycompare());

        // ts.add(new People("張三",3));
        // ts.add(new People("趙一",9));
     //  ts.add(new People("李四",4));
        // ts.add(new People("王五",5));
        // ts.add(new People("李四四",4));

        ts.add(new People("a02",3));
        ts.add(new People("a01",5));
        ts.add(new People("a39",9));
        ts.add(new People("a40",7));
        System.out.println(ts);

        Iterator i = ts.iterator();

        while(i.hasNext()) {
            People p = (People) i.next();
            System.out.println(p.getName() + "....." + p.getAge());
        }
    }
}

// 元素類實現Comparable接口，複寫compareTo方法
class People implements Comparable {
    private String name;
    private int age;

    People (String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return this.name;
    }
    public int getAge(){
        return this.age;
    } 

    public int compareTo (Object obj) {
        People p = (People) obj;
        if (this.age > p.age) {
            return 1;
        } else if (this.age == p.age){
            return this.name.compareTo(p.name);
        }
        return -1;
    }
}


// 比較器實現Comparator接口，複寫compare方法
class Mycompare implements Comparator {
    public int compare(Object o1, Object o2) {
        People p1 = (People) o1;
        People p2 = (People) o2;

        int num = p1.getName().compareTo(p2.getName());

        if (num == 0) {
            return p1.getAge() - p2.getAge();
        }
        return num;
    }
}