遍历输出map

HashMap extends AbstractMap implements Map

方式一：

public static void printMap1(Map<String, String> map) {
        System.out.println("\n方法一");
        Set<Map.Entry<String, String>> entries = map.entrySet();
        for (Map.Entry<String, String> entry : entries) {
            System.out.println(entry.getKey() + "    " + entry.getValue());
        }
    }

用transient关键字标记的成员变量不参与序列化过程。

map.entrySet()源码：

 public Set<Map.Entry<K,V>> entrySet() {
        Set<Map.Entry<K,V>> es;
        return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
    }

这里知识new一个 EntrySet

entrySet是 java中 键-值 对的集合,HashMap的成员类-EntrySet

final class EntrySet extends AbstractSet<Map.Entry<K,V>> {}

entry是map中的一个内部类

interface Entry<K,V> {       
        K getKey();   
        V getValue();
}

方式二

public static void printMap2(Map<String, String> map) {
        System.out.println("\n方法二");
        map.forEach((key, value) -> {
            System.out.println(key + "    " + value);
        });
    }

方式三

public static void printMap3(Map<String, String> map) {
        System.out.println("\n方法三");
        Set<String> keySet = map.keySet();
        for (String key : keySet) {
            System.out.println(key + "    " + map.get(key));
        }
    }

方式四

 public static void printMap4(Map<String, String> map) {
        System.out.println("\n方法四");
        Set<Map.Entry<String, String>> entries = map.entrySet();
        Iterator<Map.Entry<String, String>> iterator = entries.iterator();
        while (iterator.hasNext()) {
            Map.Entry<String, String> next = iterator.next();
            System.out.println(next.getKey() + "    " + next.getValue());
        }
    }

方式五

public static void printMap5(Map<String, String> map) {
        System.out.println("\n方法五");
        Collection<String> values = map.values();
        for (String value : values) {
            System.out.println(value);
        }
    }