03Java8Map遍历

Java8Map的遍历

遍历方式

package com.arithmetic;

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

public class Java8Map {

    public static void main(String[] args) {

        Map<String, Object> map = new HashMap<>();
        map.put("key1", "value1");
        map.put("key2", "value2");
        map.put("key3", "value3");
        map.put("key4", 4);
        map.put("key5", 5);
        map.put("key5", 'h');

        /**
         * 遍历Map的方式一
         * 通过Map.keySet遍历key和value
         */
        System.out.println("---------------------Before JAVA8 ------------------------------");
        for (String key : map.keySet()) {
            System.out.println("map.get(" + key + ") = " + map.get(key));
        }
        System.out.println("---------------------JAVA8 ------------------------------");
        map.keySet().forEach(key -> System.out.println("map.get(" + key + ") = " + map.get(key)));

        /**
         * 遍历Map第二种
         * 通过Map.entrySet使用Iterator遍历key和value
         */
        System.out.println("---------------------Before JAVA8 ------------------------------");
        Iterator<Map.Entry<String, Object>> iterator = map.entrySet().iterator();
        while (iterator.hasNext()) {
            Map.Entry<String, Object> entry = iterator.next();
            System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue());
        }
        System.out.println("---------------------JAVA8 ------------------------------");
        map.entrySet().iterator().forEachRemaining(item -> System.out.println("key:value=" + item.getKey() + ":" + item.getValue()));

        /**
         * 遍历Map第三种
         * 通过Map.entrySet遍历key和value,在大容量时推荐使用
         */
        System.out.println("---------------------Before JAVA8 ------------------------------");
        for (Map.Entry<String, Object> entry : map.entrySet()) {
            System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue());
        }
        System.out.println("---------------------JAVA8 ------------------------------");
        map.entrySet().forEach(entry -> System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue()));

        /**
         * 遍历Map第四种
         * 通过Map.values()遍历所有的value,但不能遍历key
         */
        System.out.println("---------------------Before JAVA8 ------------------------------");
        for (Object value : map.values()) {
            System.out.println("map.value = " + value);
        }
        System.out.println("---------------------JAVA8 ------------------------------");
        map.values().forEach(System.out::println);

        /**
         * 遍历Map第五种
         * 通过k,v遍历,Java8独有的
         */
        System.out.println("---------------------Only JAVA8 ------------------------------");
        map.forEach((k, v) -> System.out.println("key:value = " + k + ":" + v));
    }
    
}

推荐使用:

  • 遍历Map第三种 entrySet().forEach

  • 遍历Map第五种 forEach

    HashMap使用的是数组加链表的方式存储数据

    函数式编程方式lamada表达式

posted @ 2022-01-13 14:31  非学无以致疑  阅读(170)  评论(0编辑  收藏  举报