Map遍历

2021.03.25
第39次记录

**代码演示：**

```java
//Map集合的遍历
public class MapTest02 {
public static void main(String[] args) {
//遍历所有的key，通过遍历key，来遍历value
Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "A1");
map.put(2, "B2");
map.put(3, "C3");
map.put(4, "D4");
Set<Integer> set = map.keySet();
Iterator<Integer> it = set.iterator();
while(it.hasNext()){
Integer i = it.next();
String s = map.get(i);
System.out.println(i + " = " + s);
}
System.out.println("--------------------");
//第二种方式，foreach
for (Integer i:set){
System.out.println(i + " = " + map.get(i));
}
System.out.println("--------------------");
//第三种方式：Set<Map.Entry<K, V>> entrySet()
//这个方法是把Map集合全部转换为Set集合
//Set集合中元素的类型是：Map.Entry
Set<Map.Entry<Integer, String>> set2 = map.entrySet();
Iterator<Map.Entry<Integer, String>> it2 = set2.iterator();
while(it2.hasNext()){
Map.Entry<Integer, String> node = it2.next();
Integer key = node.getKey();
String value = node.getValue();
System.out.println(key + " = " + value);
}
System.out.println("--------------------");
//第四种方式，foreach
for (Map.Entry<Integer, String> node:set2){
System.out.println(node.getKey() + " = " + node.getValue());
}
}
}
```

输出结果：

```java
1 = A1
2 = B2
3 = C3
4 = D4
--------------------
1 = A1
2 = B2
3 = C3
4 = D4
--------------------
1 = A1
2 = B2
3 = C3
4 = D4
--------------------
1 = A1
2 = B2
3 = C3
4 = D4
```