Java8⾼效遍历map_Java8中Map的遍历⽅式总结

public class LambdaMap {
private Map map = new HashMap<>();
@Before
public void initData() {
map.put("key1", "value1");
map.put("key2", "value2");
map.put("key3", "value3");
map.put("key4", 4);
map.put("key5", 5);
map.put("key5", 'h');
}

/**
* 遍历Map的⽅式⼀
* 通过Map.keySet遍历key和value
*/
@Test
public void testErgodicWayOne() {
System.out.println("---------------------Before JAVA8 ------------------------------");
for (String key : map.keySet()) {
System.out.println("map.get(" + key + ") = " + map.get(key));
}
System.out.println("---------------------JAVA8 ------------------------------");
map.keySet().forEach(key -> System.out.println("map.get(" + key + ") = " + map.get(key)));
}

 

/**
* 遍历Map第⼆种
* 通过Map.entrySet使⽤Iterator遍历key和value
*/
@Test
public void testErgodicWayTwo() {
System.out.println("---------------------Before JAVA8 ------------------------------");
Iterator> iterator = map.entrySet().iterator();
while (iterator.hasNext()) {
Map.Entry entry = iterator.next();
System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue());
}
System.out.println("---------------------JAVA8 ------------------------------");
map.entrySet().iterator().forEachRemaining(item -> System.out.println("key:value=" + item.getKey() + ":" + item.getValue()));
}

 

/**
* 遍历Map第三种
* 通过Map.entrySet遍历key和value，在⼤容量时推荐使⽤
*/
@Test
public void testErgodicWayThree() {
System.out.println("---------------------Before JAVA8 ------------------------------");
for (Map.Entry entry : map.entrySet()) {
System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue());
}
System.out.println("---------------------JAVA8 ------------------------------");
map.entrySet().forEach(entry -> System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue()));
}

 

System.out.println("---------------------Before JAVA8 ------------------------------");
for (Object value : map.values()) {
System.out.println("map.value = " + value);
}
System.out.println("---------------------JAVA8 ------------------------------");
map.values().forEach(System.out::println); // 等价于map.values().forEach(value -> System.out.println(value));
}

 

/**
* 遍历Map第五种
* 通过k,v遍历，Java8独有的
*/
@Test
public void testErgodicWayFive() {
System.out.println("---------------------Only JAVA8 ------------------------------");
map.forEach((k, v) -> System.out.println("key:value = " + k + ":" + v));
}
}

 Java Map各遍历⽅式的性能⽐较
1. 阐述 对于Java中Map的遍历⽅式,很多⽂章都推荐使⽤entrySet,认为其⽐keySet的效率⾼很多.理由是:entrySet⽅法⼀次拿到所有key和
value的集合:⽽keySet拿到的 ...