Map一些新方法的具体使用案例

1、getOrDefault:default V getOrDefault(Object key, V defaultValue)

package com.qbb.threadpool;import java.util.HashMap;
import java.util.Map;/*** @author QiuQiu&LL (个人博客:https://www.cnblogs.com/qbbit)* @version 1.0* @date 2022-07-23  11:49* @Description:*/
public class Java8NewFeature {public static void main(String[] args) {Map<String,String> map = new HashMap<>();map.put("name", "qiuqiu");map.put("age", "22");map.put("hobby", "haha");map.put("interest", "no");/*** getOrDefault*/String orDefaultValue = getOrDefaultTest(map);System.out.println("orDefaultValue = " + orDefaultValue);}/*** getOrDefault* 如果Map中不存在该key，可以提供一个默认值，方法会返回改默认值。* 如果存在该key，返回键对应的值*/public static String getOrDefaultTest(Map<String,String> map){String orDefault = map.getOrDefault("qiu", "baoabo");return orDefault;}
}

2、forEach：default void forEach(BiConsumer<? super K, ? super V> action)

/*** forEach* 遍历map*/public static String forEachTest(Map<String, String> map) {/*** 以前的写法*/for (Map.Entry<String, String> entry : map.entrySet()) {String key = entry.getKey();String value = entry.getValue();System.out.println(key + "===" + value);}/*** 现在的写法*/map.forEach((k, v) -> System.out.println(k + "===" + v));/*** 还可以做一些中间操作*/map.forEach((k, v) -> {System.out.println(k + "===" + v);v = v + "you";map.put(k, v);});map.forEach((k, v) -> System.out.println(k + "===" + v));return null;}

3、putIfAbsent:default V putIfAbsent(K key, V value)

/*** putIfAbsent* V putIfAbsent(K key, V value)只有在不存在key值的映射或者映射值为null，才将value值赋值给key。* 否则不做修改。该方法将条件判断和赋值合二为一。*/public static String putIfAbsentTest(Map<String, String> map) {String result1 = map.put("name", "ll");System.out.println("result1 = " + result1);String result2 = map.putIfAbsent("name", "qiuqiu");System.out.println("result2 = " + result2);String name = map.get("name");System.out.println("name = " + name);String absent = map.putIfAbsent("hello", "qiuqiu");System.out.println("absent = " + absent);String hello = map.get("hello");System.out.println("hello = " + hello);return null;}

4、compute:default V compute(K key,BiFunction<? super K, ? super V, ? extends V> remappingFunction)

default V compute(K key,BiFunction<? super K, ? super V, ? extends V> remappingFunction) {Objects.requireNonNull(remappingFunction);// 获取key对应的值V oldValue = get(key);//获取新值V newValue = remappingFunction.apply(key, oldValue);// 如果新值为null，并且key存在，则删除key；否则把新值赋值给keyif (newValue == null) {// delete mappingif (oldValue != null || containsKey(key)) {// something to removeremove(key);return null;} else {// nothing to do. Leave things as they were.return null;}} else {// add or replace old mappingput(key, newValue);return newValue;}
}

5、computeIfAbsent:default V computeIfAbsent(K key,Function<? super K, ? extends V> mappingFunction)

public static void main(String[] args) {Map<String, String> map = new HashMap<>();map.put("name", "qiuqiu");map.put("age", "22");map.put("hobby", "haha");map.put("interest", "no");/* 当Map中不存在key值的映射或映射值为null时，调用mappingFunction，并在mappingFunction执行结果非null时，将结果赋值给key。*/String ifAbsent = map.computeIfAbsent("qiuqiu", k -> {return "hello:" + k;});System.out.println("ifAbsent = " + ifAbsent);}

6、merge:default V merge(K key, V value,BiFunction<? super V, ? super V, ? extends V> remappingFunction)

public static void main(String[] args) {Map<String, String> map = new HashMap<>();map.put("name", "qiuqiu");map.put("age", "22");map.put("hobby", "haha");map.put("interest", "no");/*** value和remappingFunction不能为null* 如果Map中key对应的映射不存在或者为null，* 则将value关联到key上；否则执行remappingFunction，* 如果执行结果为null则删除key的映射，否则用该结果跟key关联。*/// 给存在的key进行映射处理String merge = map.merge("name", "ll", (k, v) -> {System.out.println(k + "===" + v);return k + v;});System.out.println("merge = " + merge);// 给不存在的key,不会执行String result = map.merge("haha", "ll", (k, v) -> {System.out.println(k + "===" + v);return k + v;});System.out.println("map.get(haha) = " + map.get("haha"));System.out.println("result = " + result);}

7、remove(key,value):default boolean remove(Object key, Object value)

/*** remove* 只有在当前Map中key映射的值等于value时才删除该映射，否则什么也不做。*/public static String removeTest(Map<String, String> map) {boolean flag = map.remove("name", "qiuqiu");System.out.println("flag = " + flag);boolean flag2 = map.remove("hobby", "ll");System.out.println("flag2 = " + flag2);return null;}

8、replace:default boolean replace(K key, V oldValue, V newValue)

 /*** replace*/public static String replaceTest(Map<String, String> map){String one = map.replace("name", "haha");System.out.println("one = " + one);String two = map.replace("haha", "hehe");System.out.println("two = " + two);boolean flag = map.replace("name", "haha", "hehe");System.out.println("flag = " + flag);return null;}

9、replaceAll:default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function)

public static void main(String[] args) {Map<String, String> map = new HashMap<>();map.put("name", "qiuqiu");map.put("age", "22");map.put("hobby", "haha");map.put("interest", "no");map.replaceAll((k, v) -> {// 对 k v 进行处理if ("hobby".equals(k)) {return v.toUpperCase();}return v;});// 打印map.forEach((k, v) -> System.out.println(k + "=" + v));}

当然还有其他的方法就不一一列举了，大家可以去试一下