HashMap遍历方法总结

Posted 2021-05-18 一名不断学习的程序猿

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

public class MapOperation {
private static Map<String, String> map = new HashMap<String, String>();
static {
map.put("1", "value1");
map.put("2", "value2");
map.put("3", "value3");
map.put("4", "value4");
}

public static void method() {
    for (Map.Entry<String, String> entry : map.entrySet()) {
        System.out.println("key : " + entry.getKey());
        System.out.println("value : " + entry.getValue());
    }
}

public static void method2() {
    for (String key : map.keySet()) {
        System.out.println("key : " + key);
        System.out.println("value : " + map.get(key));
    }
}

public static void method3() {
    Iterator<HashMap.Entry<String, String>> iterator = map.entrySet().iterator();
    while (iterator.hasNext()) {
        Map.Entry<String, String> entry = iterator.next();
        System.out.println("key : " + entry.getKey());
        System.out.println("value : " + entry.getValue());
    }
}


public static void method4() {
    Iterator<String> iterator = map.keySet().iterator();
    while (iterator.hasNext()) {
        String key = iterator.next();
        System.out.println("key : " + key);
        System.out.println("value : " + map.get(key));
    }
}

public static void method5() {
    map.forEach((key, value) -> {
        System.out.println("key : " + key);
        System.out.println("value : " + value);
    });
}

//通过Map.values()遍历所有的value，但不能遍历key"
public static void method6() {
    for (String v : map.values()) {
        System.out.println("The value is " + v);
    }

}

public static void method7() {
    for (Map.Entry<String, String> entry : map.entrySet()) {
        System.out.println("Key:" + entry.getKey());
        System.out.println(" Value:" + entry.getValue());
    }
}

}