包

package java.util;

简介

An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.

结构

查询操作

// Query Operations
int size();
boolean isEmpty();
boolean containsKey(Object key);
boolean containsValue(Object value);
V get(Object key);

修改操作

// Modification Operations
V put(K key, V value);
V remove(Object key);

批量操作

// Bulk Operations
void putAll(Map<? extends K, ? extends V> m);
void clear();

查看方法

// Views
Set<K> keySet();
Collection<V> values();
Set<Map.Entry<K, V>> entrySet();

内部类 Entry

K getKey();
V getValue();
V setValue(V value);

比较和哈希

参考文章：
JAVA泛型知识（二）--> <? extends T>和<? super T>
JAVA8的java.util.function包

// Comparison and hashing
boolean equals(Object o);
int hashCode();
boolean equals(Object o);
int hashCode();
public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey();
public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue();
public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp);
public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp);

默认方法

参考文章：
java接口中的default方法

// Defaultable methods
default V getOrDefault(Object key, V defaultValue);
default void forEach(BiConsumer<? super K, ? super V> action);
default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function);
default V putIfAbsent(K key, V value);
default boolean remove(Object key, Object value);
default boolean replace(K key, V oldValue, V newValue);
default V replace(K key, V value)
default V computeIfAbsent(K key,
            Function<? super K, ? extends V> mappingFunction);
default V computeIfPresent(K key,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction);
default V computeIfPresent(K key,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction);
default V compute(K key,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction);
default V merge(K key, V value,
            BiFunction<? super V, ? super V, ? extends V> remappingFunction)