Map集合

<K,V> k代表key V代表值

Key不能重复，每一个Key对应一个值

//HashMap集合
public class E12 {
    public static void main(String[] args) {
        //创建对象
        HashMap<String, String> s = new HashMap<>();
        //添加对象
        s.put("001","周明亮");
        s.put("002","周浩然");
        s.put("003","周大我");
        //输出对象
        System.out.println(s);
    }
}

//{001=周明亮, 002=周浩然, 003=周大我}

Key是唯一的 不能重复的，但是值可以重复

import java.util.HashMap;

//HashMap集合
public class E12 {
    public static void main(String[] args) {
        //创建对象
        HashMap<String, String> s = new HashMap<>();
        //添加对象
        s.put("001","周明亮");
        s.put("002","周浩然");
        s.put("003","周明亮");
        //输出对象
        System.out.println(s);
    }
}

import java.util.HashMap;

//map集合的基本方法
public class E13 {
    public static void main(String[] args) {
        //创建对象
        HashMap<String, String> s = new HashMap<>();

        //1.添加元素
        s.put("001","周明亮");
        s.put("002","我最棒");
        s.put("003","大王");

        System.out.println(s);
        //结果：{001=周明亮, 002=我最棒, 003=大王}

        //2.删除元素
        s.remove("001");
        System.out.println(s);
        //{002=我最棒, 003=大王}

        //3.移除所有Key对应的值
        //s.clear();
        //System.out.println(s);
        //{}

        //4.判断是否包含对应的Key
        System.out.println(s.containsKey("001"));
        //false
        System.out.println(s.containsKey("002"));
        //true
        
        

    }
}

**Map集合的获取功能**

import java.util.Collection;
import java.util.HashMap;
import java.util.Set;

//Map集合的获取功能
public class E14 {
    public static void main(String[] args) {
        //创建集合对象
        HashMap<String, String> s = new HashMap<>();
        //添加值
        s.put("001","周明亮");
        s.put("002","我最棒");
        s.put("003","大王");

        //1.根据Key获取值
        System.out.println(s.get("001"));
        //周明亮

        //2.获取所有Key的集合
        Set<String> st = s.keySet();
        for (String s1 : st) {
            System.out.println(s1);
        }
        //结果//001
        //002
        //003

        //3.获得所有值的集合
        Collection<String> va = s.values();
        for (String s2 : va) {
            System.out.println(s2);
        }
        //周明亮
        //我最棒
        //大王


    }
    }

Map集合的遍历

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class E15 {
    public static void main(String[] args) {
        HashMap<String, String> s = new HashMap<>();
        s.put("001","周明亮");
        s.put("002","我最棒");
        s.put("003","大王");

        //遍历方法1
        Collection<String> va = s.values();
        for (String s1 : va) {
            System.out.println(s1);
        }
        //周明亮
        //我最棒
        //大王

        //遍历方法2
        Set<String> st = s.keySet();
        for (String s2 : st) {
            System.out.println(s.get(s2));
        }
        //周明亮
        //我最棒
        //大王

        System.out.println("========================");
        //遍历方法3
        Set<Map.Entry<String, String>> en = s.entrySet();
        for (Map.Entry<String, String> e : en) {
            System.out.println(e);
            String key = e.getKey();
            System.out.println(key);
            String value = e.getValue();
            System.out.println(value);


        }



    }
}

2021-03-16 19:41:55