java HashMap 和 LinkedHashMap

一、HashMap

1、特点

a、key value键值对

b、无序

c、无索引

d、线程不安全

e、key value可为null

2、方法

// 1.增 put(key, value)
// 2.删 remove(key)
// 3.改 put(key, value)
// 4.查 get(key)
// 5.遍历
//5.1 获取key, 根据key获取值
//5.2 获取 key-value 通过 entrySet()
// 6.是否包含key

3、案例

package com.wt.map;

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

public class Demon01 {
    public static void main(String[] args) {
        // HashMap
        HashMap<String, String> hashMap = new HashMap<>();
        // 1.增 put(key, value)
        hashMap.put("name", "小薪");
        hashMap.put("father","广智");
        hashMap.put("mother","美呀");
        hashMap.put("friend","风间");
        hashMap.put("school","双叶");
        hashMap.put("teacher","娜娜");
        System.out.println("hashMap = " + hashMap);
        // 2.删 remove(key)
        hashMap.remove("father");
        System.out.println("hashMap = " + hashMap);
        // 3.改 put(key, value)
        hashMap.put("name", "小葵");
        System.out.println("hashMap = " + hashMap);
        // 4.查 get(key)
        String school = hashMap.get("school");
        System.out.println("school = " + school);
        // 5.遍历
        //5.1 获取key, 根据key获取值
        Set<String> keySet = hashMap.keySet();
        for (String s : keySet) {
            String val = hashMap.get(s);
            System.out.println("val = " + val);
        }
        //5.2 获取 key-value 通过 entrySet()
        Set<Map.Entry<String, String>> entries = hashMap.entrySet();
        for (Map.Entry<String, String> entry : entries) {
            System.out.println(entry.getKey()+"..."+entry.getValue());
        }
        // 6.是否包含key
        boolean name = hashMap.containsKey("name");
        System.out.println("name = " + name);
    }
}

二、LinkedHashMap

1、特点

a、key value键值对

b、有序

c、无索引

d、key value可为null

e、线程不安全

2、方法

与HashMap一样