如上图:
(1)Map是映射接口,Map中存储的内容是键值对(key-value)
(2)AbstractMap是继承于Map的抽象类,实现了Map中的大部分API。
(3)SortedMap是继承于Map的接口,SortedMap中的内容是排序的键值对,排序的方法是通过比较器。
(4)NavigableMap继承于SortedMap,其中有一系列的导航方法,如“获取大于或等于某对象的键值对”等等
(5)TreeMap继承于AbstractMap和NavigableMap接口,因此TreeMap中的内容是有序的键值对。
(6)HashMap继承于AbstractMap,内容也是键值对,但不保证次序。
(7)WeakHashMap继承于AbstractMap,它和HashMap的键类型不同,WeakHashMap是弱键。
(8)HashTable继承于Directionary同时也实现了Map,因此是键值对的,但不保证次序,同时是线程安全的。
总结:
HashMap是基于”拉链法“实现的散列表,一般用于单线程,键值都可以为空,支持Iterator(迭代器)遍历
Hashtable是基于”拉链法“实现的散列表,是线程安全的,可以用于多线程程序中。支持Iterator(迭代器)遍历和Enumeration(枚举器)两种遍历方式。
WeakHashMap也是基于”拉链法“实现的散列表,同时是弱键
TreeMap 是有序的散列表,通过红黑树来实现的,键值都不能为空。
Java8的Map接口的源码:
<p>public interface Map<K,V> {<br> int size();//数目<br> boolean isEmpty();//判断是否为空<br> boolean containsKey(<a href="http://www.php.cn/wiki/60.html" target="_blank">Object</a> key);//判断是否含有某个key<br> boolean containsValue(Object value);//判断是否含有某个值<br> V get(Object key);//通过key获得value<br> V put(K key, V value);//插入键值对<br> V remove(Object key);//通过key<a href="http://www.php.cn/php/php-tp-remove.html" target="_blank">删除</a><br> void put<a href="http://www.php.cn/wiki/1483.html" target="_blank">All</a>(Map<? <a href="http://www.php.cn/wiki/166.html" target="_blank">extends</a> K, ? extends V> m);//将一个Map插入<br> void <a href="http://www.php.cn/wiki/917.html" target="_blank">clear</a>();//清空<br> <a href="http://www.php.cn/code/8209.html" target="_blank">Set</a><K> keySet();//返回key集合<br> Collection<V> values();//返回value<br> Set<Map.Entry<K, V>> entrySet();//实体集合,Map的改变会影响到它<br> interface Entry<K,V> {<br> K getKey();//获得key<br> V getValue();//获得value<br> V setValue(V value);//设置值<br> boolean equals(Object o);//判断对象是否相等<br> int hashCode();//返回hashCode<br> //比较器,比较两个key<br> public <a href="http://www.php.cn/wiki/188.html" target="_blank">static</a> <K extends Comparable<? <a href="http://www.php.cn/code/8202.html" target="_blank">super</a> K>, V> Comparator<Map.Entry<K,V>> comparingByKey() {<br> <a href="http://www.php.cn/wiki/135.html" target="_blank">return</a> (Comparator<Map.Entry<K, V>> & Serializable)<br> (c1, c2) -> c1.getKey().compareTo(c2.getKey());<br> }<br> //比较两个值<br> public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {<br> return (Comparator<Map.Entry<K, V>> & Serializable)<br> (c1, c2) -> c1.getValue().compareTo(c2.getValue());<br> }<br> //比较两个key<br> public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {<br> Objects.<a href="http://www.php.cn/wiki/136.html" target="_blank">require</a>Non<a href="http://www.php.cn/wiki/62.html" target="_blank">Null</a>(cmp);<br> return (Comparator<Map.Entry<K, V>> & Serializable)<br> (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());<br> }<br> //比较两个值<br> public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {<br> Objects.requireNonNull(cmp);<br> return (Comparator<Map.Entry<K, V>> & Serializable)<br> (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());<br> }<br> }<br> //比较map是否相等<br> boolean equals(Object o);<br> int hashCode();//hashCode<br> default V get<a href="http://www.php.cn/wiki/1360.html" target="_blank">OrD</a>efault(Object key, V defaultValue) {<br> V v;<br> return (((v = get(key)) != null) || containsKey(key))<br> ? v<br> : defaultValue;<br> }<br> default void <a href="http://www.php.cn/wiki/127.html" target="_blank">forEach</a>(BiConsumer<? super K, ? super V> <a href="http://www.php.cn/java/java-Action.html" target="_blank">action</a>) {<br> Objects.requireNonNull(action);<br> for (Map.Entry<K, V> entry : entrySet()) {<br> K k;<br> V v;<br> try {<br> k = entry.getKey();<br> v = entry.getValue();<br> } catch(IllegalState<a href="http://www.php.cn/wiki/265.html" target="_blank">Exception</a> ise) {<br> // this usually means the entry is no longer in the map.<br> throw <a href="http://www.php.cn/wiki/165.html" target="_blank">new</a> Con<a href="http://www.php.cn/wiki/1046.html" target="_blank">current</a>Mod<a href="http://www.php.cn/wiki/109.html" target="_blank">if</a>icationException(ise);<br> }<br> action.accept(k, v);<br> }<br> }<br> default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {<br> Objects.requireNonNull(function);<br> for (Map.Entry<K, V> entry : entrySet()) {<br> K k;<br> V v;<br> try {<br> k = entry.getKey();<br> v = entry.getValue();<br> } catch(IllegalStateException ise) {<br> // this usually means the entry is no longer in the map.<br> throw new ConcurrentModificationException(ise);<br> }<br><br> // ise thrown from function is not a cme.<br> v = function.apply(k, v);<br><br> try {<br> entry.setValue(v);<br> } catch(IllegalStateException ise) {<br> // this usually means the entry is no longer in the map.<br> throw new ConcurrentModificationException(ise);<br> }<br> }<br> }<br> default V putIfAbsent(K key, V value) {<br> V v = get(key);<br> if (v == null) {<br> v = put(key, value);<br> }<br><br> return v;<br> }<br> //删除某个key和value对应的对象<br> default boolean remove(Object key, Object value) {<br> Object curValue = get(key);<br> if (!Objects.equals(curValue, value) ||<br> (curValue == null && !containsKey(key))) {<br> return false;<br> }<br> remove(key);<br> return true;<br> }<br> //将某个key和oldValue对应的值替换为newValue<br> default boolean replace(K key, V oldValue, V newValue) {<br> Object curValue = get(key);<br> if (!Objects.equals(curValue, oldValue) ||<br> (curValue == null && !containsKey(key))) {<br> return false;<br> }<br> put(key, newValue);<br> return true;<br> }<br> //替换key的值<br> default V replace(K key, V value) {<br> V curValue;<br> if (((curValue = get(key)) != null) || containsKey(key)) {<br> curValue = put(key, value);<br> }<br> return curValue;<br> }<br> default V computeIfAbsent(K key,<br> Function<? super K, ? extends V> mappingFunction) {<br> Objects.requireNonNull(mappingFunction);<br> V v;<br> if ((v = get(key)) == null) {<br> V newValue;<br> if ((newValue = mappingFunction.apply(key)) != null) {<br> put(key, newValue);<br> return newValue;<br> }<br> }<br><br> return v;<br> }<br> default V computeIfPresent(K key,<br> BiFunction<? super K, ? super V, ? extends V> remappingFunction) {<br> Objects.requireNonNull(remappingFunction);<br> V oldValue;<br> if ((oldValue = get(key)) != null) {<br> V newValue = remappingFunction.apply(key, oldValue);<br> if (newValue != null) {<br> put(key, newValue);<br> return newValue;<br> } <a href="http://www.php.cn/wiki/111.html" target="_blank">else</a> {<br> remove(key);<br> return null;<br> }<br> } else {<br> return null;<br> }<br> }<br> default V compute(K key,<br> BiFunction<? super K, ? super V, ? extends V> remappingFunction) {<br> Objects.requireNonNull(remappingFunction);<br> V oldValue = get(key);<br><br> V newValue = remappingFunction.apply(key, oldValue);<br> if (newValue == null) {<br> // <a href="http://www.php.cn/wiki/1298.html" target="_blank">delete</a> mapping<br> if (oldValue != null || containsKey(key)) {<br> // something to remove<br> remove(key);<br> return null;<br> } else {<br> // nothing to do. Leave things as they were.<br> return null;<br> }<br> } else {<br> // add or replace old mapping<br> put(key, newValue);<br> return newValue;<br> }<br> }<br> default V merge(K key, V value,<br> BiFunction<? super V, ? super V, ? extends V> remappingFunction) {<br> Objects.requireNonNull(remappingFunction);<br> Objects.requireNonNull(value);<br> V oldValue = get(key);<br> V newValue = (oldValue == null) ? value :<br> remappingFunction.apply(oldValue, value);<br> if(newValue == null) {<br> remove(key);<br> } else {<br> put(key, newValue);<br> }<br> return newValue;<br> }<br>}<br></p>
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