Map接口方法

Map接口和常用方法

Map体系的继承图

Map接口常用方法

1. put：添加
2. remove:根据健删除映射关系
3. get: 根据键获取值
4. size:获取元素个数
5. isEmpty:判断个数是否为0
6. clear:清除
7. containsKey:查找键是否存在

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

public class MapMethod {
    public static void main(String[] args) {
        //map接口常用方法
        Map map = new HashMap();

        map.put("test1", new Book("", 100));//ok
        map.put("test1", "test2");//替换
        map.put("test3", "test4");//ok
        map.put("test5", "test4");//ok
        map.put("test6", null);//ok
        map.put(null, "test7");//ok
        map.put("test8", "test9");//ok

        System.out.println("map = " + map);

        //remove:根据健删除映射关系
        map.remove(null);
        System.out.println("map = " + map);

        //get: 根据键获取值
        Object test8 = map.get("test8");

        System.out.println("test8 = " + test8);

        //size:获取元素个数
        System.out.println("k-v = " + map.size());

        //isEmpty:判断个数是否为0
        System.out.println(map.isEmpty());//F

        //clear:清除
        map.clear();
        System.out.println("map = " + map);

        //containsKey:查找键是否存在
        System.out.println(map.containsKey("wsh"));//F

        map.put("wsh", "wsh的老婆");
        System.out.println(map.containsKey("wsh"));//T

    }
}

class Book {
    private String name;
    private double price;

    public Book(String name, double price) {
        this.name = name;
        this.price = price;
    }
}