Map遍历常见的四种方式

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Map遍历常见的四种方式

代码如下（示例）：

package com.lanhuigu.map;

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

/**
 * @className: MapString
 * @author: Jiuzhoumu96
 * @date: 2022/06/07 14:16
 */
public class MapString {

    public static void main(String[] args) {

        Map<String, String> map = new HashMap<>();
        map.put("k1", "v1");
        map.put("k2", "v2");
        map.put("k3", "v3");
        map.put("k4", "v4");
        map.put("k5", "v5");

        method1(map);
        method2(map);
        method3(map);
        method4(map);

    }

    private static void method1(Map<String, String> map) {
        // 方式一、for循环
        for (Map.Entry<String, String> entry : map.entrySet()) {
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println("key = " + key + ", value = " + value);
        }
    }

    private static void method2(Map<String, String> map) {
        // 方式二、迭代
        Set set = map.entrySet();
        Iterator iterator = set.iterator();
        while (iterator.hasNext()) {
            Map.Entry<String, String> entry = (Map.Entry<String, String>) iterator.next();
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println("key = " + key + ", value = " + value);
        }
    }
    
    private static void method3(Map<String, String> map) {
        // 方式三、keySet()迭代
        Iterator iterator = map.keySet().iterator();
        while (iterator.hasNext()) {
            String key = iterator.next().toString();
            String value = map.get(key);
            System.out.println("key = " + key + ", value = " + value);
        }
    }    
    
    private static void method4(Map<String, String> map) {
        // 方式四、entrySet()迭代
        Iterator iterator = map.entrySet().iterator();
        while (iterator.hasNext()) {
            Map.Entry entry = (Map.Entry) iterator.next();
            String key=entry.getKey().toString();
            String value=entry.getValue().toString();
            System.out.println("key = " + key + ", value = " + value);
        }
    }
    
}

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总结

  更习惯使用for循环的方式。