java 集合（Set2）

TreeSet:

1.向TreeSet添加元素时

如果元素具有自然特性，那么就按照元素的自然顺序的特点进行排序储存。

如果不具备，就要实现Compareable接口中的compareTo() 方法。

可以直接实现Compareable接口，但最好自己定义比较器类。

2.TreeSet的底层实现是红黑树，也叫二叉树，集合中的元素一个个进行比较时

当把拿出来的第一个元素当成树根，依次拿其它元素进行比较如果大于树根

就放在其右支，小于则放在其左支，如此迭代，直到所有元素被比较完，安放完。

注意：在二叉树中出现3个元素，还未形成二叉结构时，就要重新排列，就是把

根和支的位置改变了。

（1， 2，3，4）   （a,  b,  c, d ）自然顺序

import java.util.*;
import java.util.ListIterator;
public class ex12 {
    public static void main(String[] args) {

        TreeSet set = new TreeSet();
        set.add(new Emp(100, "Tom", 100));
        set.add(new Emp(101, "Tom", 400));
        set.add(new Emp(109, "Tom", 100));//Ctrl + d
        set.add(new Emp(109, "Tom", 99));//Ctrl + d
        set.add(new Emp(209, "Tom", 130));//Ctrl + d
        System.out.println(set);

    }
}

class Emp implements Comparable{
    int id;
    String name;
    int money;

    public Emp(int id, String name, int money) {
        this.id = id;
        this.name = name;
        this.money = money;
    }

    @Override
    public String toString() {
        return "{ id = " + this.id +  " ,name = " + this.name + " ,money = " + money + " }";
    }

    @Override//Ctrl + O
    public int compareTo(Object o) {
     Emp e = (Emp)o;
        return this.money - e.money ;
    }
}

[{ id = 109 ,name = Tom ,money = 99 }, { id = 100 ,name = Tom ,money = 100 }, { id = 209 ,name = Tom ,money = 130 }, { id = 101 ,name = Tom ,money = 400 }]

Process finished with exit code 0

import java.util.*;
import java.util.ListIterator;
public class ex12 {
    public static void main(String[] args) {

        MyCompare my = new MyCompare();
        TreeSet set = new TreeSet(my);//创建构造器时传入构造器***********
        set.add(new Emp(100, "Tom", 100));
        set.add(new Emp(101, "Tom", 400));
        set.add(new Emp(109, "Tom", 100));//Ctrl + d
        set.add(new Emp(109, "Tom", 99));
        set.add(new Emp(209, "Tom", 130));
        System.out.println(set);

    }
}

class Emp {
    int id;
    String name;
    int money;

    public Emp(int id, String name, int money) {
        this.id = id;
        this.name = name;
        this.money = money;
    }

    @Override
    public String toString() {
        return "{ id = " + this.id +  " ,name = " + this.name + " ,money = " + money + " }";
    }
}

//自定义构造器
class MyCompare implements Comparator<Emp> {
    @Override
    public int compare(Emp o1, Emp o2) {
        return o1.id - o2.id;
    }
}
//按id排序

[{ id = 100 ,name = Tom ,money = 100 }, { id = 101 ,name = Tom ,money = 400 }, { id = 109 ,name = Tom ,money = 100 }, { id = 209 ,name = Tom ,money = 130 }]

Process finished with exit code 0