Java-Map源码分析及特性

public interface Map<K,V> {
int size();//数目
boolean isEmpty();//判断是否为空
boolean containsKey(Object key);//判断是否含有某个key
boolean containsValue(Object value);//判断是否含有某个值
V get(Object key);//通过key获得value
V put(K key, V value);//插入键值对
V remove(Object key);//通过key删除
void putAll(Map<? extends K, ? extends V> m);//将一个Map插入
void clear();//清空
Set<K> keySet();//返回key集合
Collection<V> values();//返回value
Set<Map.Entry<K, V>> entrySet();//实体集合，Map的改变会影响到它
interface Entry<K,V> {
K getKey();//获得key
V getValue();//获得value
V setValue(V value);//设置值
boolean equals(Object o);//判断对象是否相等
int hashCode();//返回hashCode
        //比较器，比较两个key
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());
}
//比较两个值
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());
}
//比较两个key
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());
}
//比较两个值
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());
}
    }
//比较map是否相等
boolean equals(Object o);
    int hashCode();//hashCode
default V getOrDefault(Object key, V defaultValue) {
V v;
        return (((v = get(key)) != null) || containsKey(key))
                ? v
                : defaultValue;
}
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);
}
    }
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);
}
        }
    }
default V putIfAbsent(K key, V value) {
V v = get(key);
        if (v == null) {
            v = put(key, value);
}

return v;
}
//删除某个key和value对应的对象
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;
}
//将某个key和oldValue对应的值替换为newValue
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;
}
//替换key的值
default V replace(K key, V value) {
V curValue;
        if (((curValue = get(key)) != null) || containsKey(key)) {
            curValue = put(key, value);
}
return curValue;
}
default V computeIfAbsent(K key,
Function<? super K, ? extends V> mappingFunction) {
        Objects.requireNonNull(mappingFunction);
V v;
        if ((v = get(key)) == null) {
V newValue;
            if ((newValue = mappingFunction.apply(key)) != null) {
                put(key, newValue);
                return newValue;
}
        }

return v;
}
default V computeIfPresent(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
V oldValue;
        if ((oldValue = get(key)) != null) {
V newValue = remappingFunction.apply(key, oldValue);
            if (newValue != null) {
                put(key, newValue);
                return newValue;
} else {
                remove(key);
                return null;
}
        } else {
return null;
}
    }
default V compute(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
V oldValue = get(key);

V newValue = remappingFunction.apply(key, oldValue);
        if (newValue == null) {
// delete mapping
if (oldValue != null || containsKey(key)) {
// something to remove
remove(key);
                return null;
} else {
// nothing to do. Leave things as they were.
return null;
}
        } else {
// add or replace old mapping
put(key, newValue);
            return newValue;
}
    }
default V merge(K key, V value,
BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
        Objects.requireNonNull(remappingFunction);
Objects.requireNonNull(value);
V oldValue = get(key);
V newValue = (oldValue == null) ? value :
                remappingFunction.apply(oldValue, value);
        if(newValue == null) {
            remove(key);
} else {
            put(key, newValue);
}
return newValue;
}
}

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