HashMap<String, String> map = new HashMap<>();
 map.put("name", "cookie");
 map.put("age", "18");
 map.put("sex", "女");
 String name = map.getOrDefault("name", "random");
 System.out.println(name);// cookie，map中存在name,獲得name對(duì)應(yīng)的value
 int score = map.getOrDefault("score", 80);
 System.out.println(score);// 80，map中不存在score,使用默認(rèn)值80

//若傳入的key對(duì)應(yīng)的value為null或者key不存在Map中,則返回defaultValue
1. default V getOrDefault(Object key, V defaultValue)

//遍歷Map集合，方法比較爽，省的自己寫(xiě)迭代器了
2. default void forEach(BiConsumer<? super K, ? super V> action)

//全部修改map的value值，修改的值取決于傳入Lambda的返回值
3. default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) 

//若key對(duì)應(yīng)的Value為空或者null,則使用value替代
4. default V putIfAbsent(K key, V value)

//若傳入的value和map中key對(duì)應(yīng)的value相等，則刪除，返回true，否者，返回false
5. default boolean remove(Object key, Object value) 

//oldValue和Map中key對(duì)應(yīng)的value相等，或者M(jìn)ap不包含key，則返回false,否則想key，newValue存放進(jìn)Map
6. default boolean replace(K key, V oldValue, V newValue)

oldValue和Map中key對(duì)應(yīng)的value相等，或者M(jìn)ap不包含key，則返回false,否則想key，newValue替換進(jìn)Map
7. default V replace(K key, V value)
8. default V computeIfAbsent(K key,
      Function<? super K, ? extends V> mappingFunction)

9. default V computeIfPresent(K key,
      BiFunction<? super K, ? super V, ? extends V> remappingFunction)
10.  default V compute(K key,
      BiFunction<? super K, ? super V, ? extends V> remappingFunction) 
11. default V merge(K key, V value,
      BiFunction<? super V, ? super V, ? extends V> remappingFunction)