Map的遍历

Map是我们常用的数据容器，常用的有以下几种遍历方式，代码如下：

package Map;

import java.util.*;

/**
 * @author o_0sky
 * @date 2019/2/15 0:37
 */
public class MapTest {
    public static void main(String[] args) {
        Map<Integer, String> map = new HashMap<Integer, String>();
        map.put(1, "a");
        map.put(2, "b");
        map.put(3, "c");
    }

    //①通过Map.keyset遍历key和value
    private static void method1(Map<Integer, String> map) {
        Set<Integer> set1 = map.keySet();
        for (Integer key1 : set1) {
            String value1 = map.get(key1);
            System.out.println("key" + "=" + key1 + "," + "value" + "=" + value1);
        }
    }

    //②通过Map.entrySet使用迭代器遍历key和value
    private static void method2(Map<Integer, String> map) {
        //生成迭代器
        Set<Map.Entry<Integer, String>> set2 = map.entrySet();
        Iterator<Map.Entry<Integer, String>> it = set2.iterator();
        while (it.hasNext()) {
            Map.Entry<Integer, String> entry = it.next();
            Integer key2 = entry.getKey();
            String value2 = entry.getValue();
            System.out.println("key" + "=" + key2 + "," + "value" + "=" + value2);
        }
    }

    //③通过Map.entrySet遍历key和value
    private static void method3(Map<Integer, String> map) {
        Set<Map.Entry<Integer, String>> set3 = map.entrySet();
        for (Map.Entry<Integer, String> entry : set3) {
            Integer key3 = entry.getKey();
            String value3 = entry.getValue();
            System.out.println("key" + "=" + key3 + "," + "value" + "=" + value3);
        }
    }

    //④直接通过Map.values遍历所有的value，但不能遍历key
    private static void method4(Map<Integer, String> map) {
        Collection<String> values = map.values();
        for (String value : values) {
            System.out.println("value" + "=" + value);
        }
    }
}