java集合框架复习----（3）Set

文章目录

• 四、set集合
• • 1、hashSet【重点】
  • 2、TreeSet

四、set集合

无序、无下标、元素不可重复

1、hashSet【重点】

== 数组+链表+红黑树==

• 基于hashcode计算元素存储位置
• 当哈希吗一样的时候，调用equals，如果为true,拒接存入

package com.zheng.demo3;

import java.util.HashSet;
import java.util.Iterator;

public class MySet {
    public static void main(String[] args) {
        
        //创建集合框架
        HashSet<String> set = new HashSet<>();

        //添加数据
        set.add("1-小红");
        set.add("2-小明");
        set.add("3-小白");
        set.add("4-小黑");
        set.add("5-小红");
        set.add("1-小红");

        //迭代器迭代集合元素 遍历
        Iterator<String> iterator = set.iterator();
      
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }

    }
}

实体类

package com.zheng.demo3;

public class School {
    private int id;
    private String name;

    public School() {

    }

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

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "School{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

package com.zheng.demo3;

import java.util.HashSet;
import java.util.Iterator;

public class TestSet {
    public static void main(String[] args) {

        //1、创建集合容器
        HashSet<School> schools = new HashSet<>();

        //创建对象
        School school1 = new School(1, "清华大学");
        School school2 = new School(2, "北京大学");
        School school3 = new School(3, "浙江大学");

        //3、放入集合

        schools.add(school1);
        schools.add(school2);
        schools.add(school3);
        schools.add(new School(2,"北京大学"));

        //4、遍历

        Iterator<School> iterator = schools.iterator();
        while (iterator.hasNext()){
            School school=iterator.next();
            System.out.println(school);
        }


    }
}

2、TreeSet

存储结构：红黑树

• 要实现comparable接口，重写里边的方法，返回0代表元素重复
• 元素不重复
• 元素自动排序

package com.zheng.demo3;

import java.util.Iterator;
import java.util.TreeSet;

public class MyTree {
    public static void main(String[] args) {

        //1、创建一个集合
        TreeSet treeSet = new TreeSet();

        //2、加入元素
        treeSet.add(1);
        treeSet.add(3);
        treeSet.add(2);
        treeSet.add(4);
        treeSet.add(3);


        //3、迭代遍历
        Iterator iterator = treeSet.iterator();
        while (iterator.hasNext()) {
            int i = (int) iterator.next();
            System.out.println(i);
        }


    }
}

TreeSet案例：排列字符串的顺序

package com.zheng.demo3;

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

public class MyTreeSet {
    public static void main(String[] args) {
        //匿名内部类
        TreeSet<String> set = new TreeSet<>(new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                int n1 = o1.length() - o2.length();
                int n2 = o1.compareTo(o2);
                return n1 == 0 ? n2 : n1;
            }

        });


        set.add("he");
        set.add("hhhhh");
        set.add("jdjdjkdkk");
        set.add("djdj");


        Iterator<String> iterator = set.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}

comparator：定制比较器