interface , and the content stored in Map is a key-value pair (key-value)
(2) AbstractMap isInherited from Map's abstract class, which implements most of the API in Map.
(3) SortedMap is an interface inherited from Map. The content in SortedMap is sorted key-value pairs, and the sorting method is through a comparator. (4) NavigableMap inherits from SortedMap, which has a series of navigation methods, such as "get key-value pairs greater than or equal to a certainobject" etc.
(5 ) TreeMap inherits from the AbstractMap and NavigableMap interfaces, so the contents in TreeMap are ordered key-value pairs. (6) HashMap inherits from AbstractMap, and the content is also a key-value pair, but the order is not guaranteed. (7) WeakHashMap inherits from AbstractMap, and its key type is different from HashMap. WeakHashMap is a weak key. (8) HashTable inherits from Summary: HashMap is a hash table based on the "zipper method". It is generally used in single threads. The key values can be empty and supports Iterator (iterator) traversalHashtable is a hash table implemented based on the "zipper method". It is thread-safe and can be used in multi-threaded programs. Supports two traversal methods: Iterator traversal and Enumeration. WeakHashMap is also a hash table based on the "zipper method" and is also a weak key. TreeMap is an ordered hash table, implemented through a red-black tree, and the key values cannot be empty. .
<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>The above is the detailed content of Detailed explanation of sample code for Map in Java collection. For more information, please follow other related articles on the PHP Chinese website!
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