Map接口源码

//返回Map中key-value的数量
int size();


//判断Map集合是否为空，是根据key-value的数量判断，如果size()返回为0，
//则此方法返回true，反之，返回false
boolean isEmpty();

//对于一个给定的key，判断Map中是否已经存在此key，存在返回true，否则返回false
boolean containsKey(Object key);


//一个Map可能存在多个(或一个)key存储的value相同，则返回true；
//如果不存在相应的key-value，则返回false
boolean containsValue(Object value);


//根据给定的key找到对应的value并返回
V get(Object key);


//将一个key-value存放在Map当中
V put(K key, V value);


//给定key，首先找到Map中的key-value，然后清除Map中的key-value，返回对应的value
V remove(Object key);


//给定一个Map集合m，将m中所有的key-value，添加到this Map当中
void putAll(Map<? extends K, ? extends V> m);


//清楚Map中所有的key-value
void clear();


//返回Map中所有key-value的key的集合
Set<K> keySet();


//返回Map中所有的key-value的value集合
Collection<V> values();


//将Map中的key-value保存在Set集合中
Set<Map.Entry<K, V>> entrySet();

Map的数据结构

interface Entry<K,V> {

        K getKey();


        V getValue();


        V setValue(V value);

        /**
         * Compares the specified object with this entry for equality.
         * Returns <tt>true</tt> if the given object is also a map entry and
         * the two entries represent the same mapping.  More formally, two
         * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping
         * if<pre>
         *     (e1.getKey()==null ?
         *      e2.getKey()==null : e1.getKey().equals(e2.getKey()))  &amp;&amp;
         *     (e1.getValue()==null ?
         *      e2.getValue()==null : e1.getValue().equals(e2.getValue()))
         * </pre>
         * This ensures that the <tt>equals</tt> method works properly across
         * different implementations of the <tt>Map.Entry</tt> interface.

        boolean equals(Object o);

        /**
         * Returns the hash code value for this map entry.  The hash code
         * of a map entry <tt>e</tt> is defined to be: <pre>
         *     (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
         *     (e.getValue()==null ? 0 : e.getValue().hashCode())
         * </pre>
         * This ensures that <tt>e1.equals(e2)</tt> implies that
         * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
         * <tt>e1</tt> and <tt>e2</tt>, as required by the general
         * contract of <tt>Object.hashCode</tt>

        int hashCode();


        public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey() {
            return (Comparator<Map.Entry<K, V>> & Serializable)
                (c1, c2) -> c1.getKey().compareTo(c2.getKey());
        }


        public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {
            return (Comparator<Map.Entry<K, V>> & Serializable)
                (c1, c2) -> c1.getValue().compareTo(c2.getValue());
        }


        public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
            Objects.requireNonNull(cmp);
            return (Comparator<Map.Entry<K, V>> & Serializable)
                (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
        }


        public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
            Objects.requireNonNull(cmp);
            return (Comparator<Map.Entry<K, V>> & Serializable)
                (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
        }
    }

默认方法

default void forEach(BiConsumer<? super K, ? super V> action) {
        Objects.requireNonNull(action);
        for (Map.Entry<K, V> entry : entrySet()) {
            K k;
            V v;
            try {
                k = entry.getKey();
                v = entry.getValue();
            } catch(IllegalStateException ise) {
                // this usually means the entry is no longer in the map.
                throw new ConcurrentModificationException(ise);
            }
            action.accept(k, v);
        }
    }

2

default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
        Objects.requireNonNull(function);
        for (Map.Entry<K, V> entry : entrySet()) {
            K k;
            V v;
            try {
                k = entry.getKey();
                v = entry.getValue();
            } catch(IllegalStateException ise) {
                // this usually means the entry is no longer in the map.
                throw new ConcurrentModificationException(ise);
            }

            // ise thrown from function is not a cme.
            v = function.apply(k, v);

            try {
                entry.setValue(v);
            } catch(IllegalStateException ise) {
                // this usually means the entry is no longer in the map.
                throw new ConcurrentModificationException(ise);
            }
        }
    }

3

default V putIfAbsent(K key, V value) {
        V v = get(key);
        if (v == null) {
            v = put(key, value);
        }

        return v;
    }

4

default boolean remove(Object key, Object value) {
        Object curValue = get(key);
        if (!Objects.equals(curValue, value) ||
            (curValue == null && !containsKey(key))) {
            return false;
        }
        remove(key);
        return true;
    }

default boolean replace(K key, V oldValue, V newValue) {
        Object curValue = get(key);
        if (!Objects.equals(curValue, oldValue) ||
            (curValue == null && !containsKey(key))) {
            return false;
        }
        put(key, newValue);
        return true;
    }