Map遍历的四种方式

Map遍历的四种方式

package com.test;

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

/**
 * Map遍历
 *
 * @author hkk
 */
public class MapTest {

    public static void main(String[] args) {

        methodOne(initMap());

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

        methodTwo(initMap());

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

        methodThree(initMap());

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

        methodFour(initMap());
    }

    /**
     * 初始化map
     *
     * @return map
     */
    private static Map<String, String> initMap() {

        Map<String, String> map = new HashMap<>(16);

        map.put("1", "one");
        map.put("2", "two");
        map.put("3", "three");
        map.put("4", "four");
        map.put("5", "five");
        map.put("6", "six");

        return map;
    }

    /**
     * 方法一: 最常用最可取的方式,在键值都需要时使用
     *
     * @param map map
     */
    private static void methodOne(Map<String, String> map) {
        for (Map.Entry<String, String> entry : map.entrySet()) {
            System.out.println("key = " + entry.getKey() + ", value = " + entry.getValue());
        }
    }

    /**
     * 方法二: for-each循环中遍历
     *
     * @param map map
     */
    private static void methodTwo(Map<String, String> map) {
        // 遍历map中的键
        for (String key : map.keySet()) {
            System.out.println("key = " + key);
        }
        // 遍历map中的值
        for (String value : map.values()) {
            System.out.println("value = " + value);
        }
    }

    /**
     * 方法三: 使用iterator遍历
     *
     * @param map map
     */
    private static void methodThree(Map<String, String> map) {
        Iterator<Map.Entry<String, String>> entryIterator = map.entrySet().iterator();
        while (entryIterator.hasNext()) {
            Map.Entry<String, String> entry = entryIterator.next();
            System.out.println("key = " + entry.getKey() + ", value = " + entry.getValue());
        }
    }

    /**
     * 方法四: 通过键找值遍历(效率低)
     *
     * @param map map
     */
    private static void methodFour(Map<String, String> map) {
        for (String key : map.keySet()) {
            System.out.println("key = " + key + ", value = " + map.get(key));
        }
    }
}