Java中遍历Map的多种方法示例及优缺点总结

public class TestMap {
 public static Map<Integer, Integer> map = new HashMap<Integer, Integer>();
}

 // KeySet 获取key
 public void testKeySet() {
 for (Integer key : map.keySet()) {
  System.out.println(key);
 }
 }
 // values 获取value
 public void testValues() {
 for (Integer value : map.values()) {
  System.out.println(value);
 }
 }

 // keySet get(key) 获取key and value
 public void testKeySetAndGetKey() {
 for (Integer key : map.keySet()) {
  System.out.println(key + ":" + map.get(key));
 }
 }

 // entrySet 获取key and value
 public void testEntry() {
 for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
  System.out.println(entry.getKey() + ":" + entry.getValue());
 }
 }

 // Iterator entrySet 获取key and value
 public void testIterator() {
 Iterator<Map.Entry<Integer, Integer>> it = map.entrySet().iterator();
 while (it.hasNext()) {
  Map.Entry<Integer, Integer> entry = it.next();
  System.out.println(entry.getKey() + ":" + entry.getValue());
  // it.remove(); 删除元素
 }
 }

 // Lambda 获取key and value
 public void testLambda() {
 map.forEach((key, value) -> {
  System.out.println(key + ":" + value);
 });
 }

 static {
 for (int i = 0; i < 100000; i++) {
  map.put(i, 1);
 }
 }

KeySet：   392
Values：   320
keySet get(key)： 552
entrySet：   465
entrySet Iterator：508
Lambda：   536