java8 map遍历

使用JAV8 带来的map遍历方式使遍历非常简单

public class LambdaMap {

private Map<String, Object> 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<Map.Entry<String, Object>> iterator = map.entrySet().iterator();

while (iterator.hasNext()) {

Map.Entry<String, Object> 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<String, Object> 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()));

}

/**

* 遍历Map第四种

* 通过Map.values()遍历所有的value,但不能遍历key

*/

@Test

public void testErgodicWayFour() {

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));

}

}

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