| /* |
| * Copyright (c) 1997, 2006, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package java.util; |
| |
| |
| import java.io.Serializable; |
| import java.util.function.BiConsumer; |
| import java.util.function.BiFunction; |
| import java.util.function.Function; |
| |
| |
| /** |
| * An object that maps keys to values. A map cannot contain duplicate keys; |
| * each key can map to at most one value. |
| * |
| * <p>This interface takes the place of the <tt>Dictionary</tt> class, which |
| * was a totally abstract class rather than an interface. |
| * |
| * <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which |
| * allow a map's contents to be viewed as a set of keys, collection of values, |
| * or set of key-value mappings. The <i>order</i> of a map is defined as |
| * the order in which the iterators on the map's collection views return their |
| * elements. Some map implementations, like the <tt>TreeMap</tt> class, make |
| * specific guarantees as to their order; others, like the <tt>HashMap</tt> |
| * class, do not. |
| * |
| * <p>Note: great care must be exercised if mutable objects are used as map |
| * keys. The behavior of a map is not specified if the value of an object is |
| * changed in a manner that affects <tt>equals</tt> comparisons while the |
| * object is a key in the map. A special case of this prohibition is that it |
| * is not permissible for a map to contain itself as a key. While it is |
| * permissible for a map to contain itself as a value, extreme caution is |
| * advised: the <tt>equals</tt> and <tt>hashCode</tt> methods are no longer |
| * well defined on such a map. |
| * |
| * <p>All general-purpose map implementation classes should provide two |
| * "standard" constructors: a void (no arguments) constructor which creates an |
| * empty map, and a constructor with a single argument of type <tt>Map</tt>, |
| * which creates a new map with the same key-value mappings as its argument. |
| * In effect, the latter constructor allows the user to copy any map, |
| * producing an equivalent map of the desired class. There is no way to |
| * enforce this recommendation (as interfaces cannot contain constructors) but |
| * all of the general-purpose map implementations in the JDK comply. |
| * |
| * <p>The "destructive" methods contained in this interface, that is, the |
| * methods that modify the map on which they operate, are specified to throw |
| * <tt>UnsupportedOperationException</tt> if this map does not support the |
| * operation. If this is the case, these methods may, but are not required |
| * to, throw an <tt>UnsupportedOperationException</tt> if the invocation would |
| * have no effect on the map. For example, invoking the {@link #putAll(Map)} |
| * method on an unmodifiable map may, but is not required to, throw the |
| * exception if the map whose mappings are to be "superimposed" is empty. |
| * |
| * <p>Some map implementations have restrictions on the keys and values they |
| * may contain. For example, some implementations prohibit null keys and |
| * values, and some have restrictions on the types of their keys. Attempting |
| * to insert an ineligible key or value throws an unchecked exception, |
| * typically <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. |
| * Attempting to query the presence of an ineligible key or value may throw an |
| * exception, or it may simply return false; some implementations will exhibit |
| * the former behavior and some will exhibit the latter. More generally, |
| * attempting an operation on an ineligible key or value whose completion |
| * would not result in the insertion of an ineligible element into the map may |
| * throw an exception or it may succeed, at the option of the implementation. |
| * Such exceptions are marked as "optional" in the specification for this |
| * interface. |
| * |
| * <p>This interface is a member of the |
| * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| * Java Collections Framework</a>. |
| * |
| * <p>Many methods in Collections Framework interfaces are defined |
| * in terms of the {@link Object#equals(Object) equals} method. For |
| * example, the specification for the {@link #containsKey(Object) |
| * containsKey(Object key)} method says: "returns <tt>true</tt> if and |
| * only if this map contains a mapping for a key <tt>k</tt> such that |
| * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should |
| * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt> |
| * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to |
| * be invoked for any key <tt>k</tt>. Implementations are free to |
| * implement optimizations whereby the <tt>equals</tt> invocation is avoided, |
| * for example, by first comparing the hash codes of the two keys. (The |
| * {@link Object#hashCode()} specification guarantees that two objects with |
| * unequal hash codes cannot be equal.) More generally, implementations of |
| * the various Collections Framework interfaces are free to take advantage of |
| * the specified behavior of underlying {@link Object} methods wherever the |
| * implementor deems it appropriate. |
| * |
| * @param <K> the type of keys maintained by this map |
| * @param <V> the type of mapped values |
| * |
| * @author Josh Bloch |
| * @see HashMap |
| * @see TreeMap |
| * @see Hashtable |
| * @see SortedMap |
| * @see Collection |
| * @see Set |
| * @since 1.2 |
| */ |
| public interface Map<K,V> { |
| // Query Operations |
| |
| /** |
| * Returns the number of key-value mappings in this map. If the |
| * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns |
| * <tt>Integer.MAX_VALUE</tt>. |
| * |
| * @return the number of key-value mappings in this map |
| */ |
| int size(); |
| |
| /** |
| * Returns <tt>true</tt> if this map contains no key-value mappings. |
| * |
| * @return <tt>true</tt> if this map contains no key-value mappings |
| */ |
| boolean isEmpty(); |
| |
| /** |
| * Returns <tt>true</tt> if this map contains a mapping for the specified |
| * key. More formally, returns <tt>true</tt> if and only if |
| * this map contains a mapping for a key <tt>k</tt> such that |
| * <tt>(key==null ? k==null : key.equals(k))</tt>. (There can be |
| * at most one such mapping.) |
| * |
| * @param key key whose presence in this map is to be tested |
| * @return <tt>true</tt> if this map contains a mapping for the specified |
| * key |
| * @throws ClassCastException if the key is of an inappropriate type for |
| * this map |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified key is null and this map |
| * does not permit null keys |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| */ |
| boolean containsKey(Object key); |
| |
| /** |
| * Returns <tt>true</tt> if this map maps one or more keys to the |
| * specified value. More formally, returns <tt>true</tt> if and only if |
| * this map contains at least one mapping to a value <tt>v</tt> such that |
| * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation |
| * will probably require time linear in the map size for most |
| * implementations of the <tt>Map</tt> interface. |
| * |
| * @param value value whose presence in this map is to be tested |
| * @return <tt>true</tt> if this map maps one or more keys to the |
| * specified value |
| * @throws ClassCastException if the value is of an inappropriate type for |
| * this map |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified value is null and this |
| * map does not permit null values |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| */ |
| boolean containsValue(Object value); |
| |
| /** |
| * Returns the value to which the specified key is mapped, |
| * or {@code null} if this map contains no mapping for the key. |
| * |
| * <p>More formally, if this map contains a mapping from a key |
| * {@code k} to a value {@code v} such that {@code (key==null ? k==null : |
| * key.equals(k))}, then this method returns {@code v}; otherwise |
| * it returns {@code null}. (There can be at most one such mapping.) |
| * |
| * <p>If this map permits null values, then a return value of |
| * {@code null} does not <i>necessarily</i> indicate that the map |
| * contains no mapping for the key; it's also possible that the map |
| * explicitly maps the key to {@code null}. The {@link #containsKey |
| * containsKey} operation may be used to distinguish these two cases. |
| * |
| * @param key the key whose associated value is to be returned |
| * @return the value to which the specified key is mapped, or |
| * {@code null} if this map contains no mapping for the key |
| * @throws ClassCastException if the key is of an inappropriate type for |
| * this map |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified key is null and this map |
| * does not permit null keys |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| */ |
| V get(Object key); |
| |
| // Modification Operations |
| |
| /** |
| * Associates the specified value with the specified key in this map |
| * (optional operation). If the map previously contained a mapping for |
| * the key, the old value is replaced by the specified value. (A map |
| * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only |
| * if {@link #containsKey(Object) m.containsKey(k)} would return |
| * <tt>true</tt>.) |
| * |
| * @param key key with which the specified value is to be associated |
| * @param value value to be associated with the specified key |
| * @return the previous value associated with <tt>key</tt>, or |
| * <tt>null</tt> if there was no mapping for <tt>key</tt>. |
| * (A <tt>null</tt> return can also indicate that the map |
| * previously associated <tt>null</tt> with <tt>key</tt>, |
| * if the implementation supports <tt>null</tt> values.) |
| * @throws UnsupportedOperationException if the <tt>put</tt> operation |
| * is not supported by this map |
| * @throws ClassCastException if the class of the specified key or value |
| * prevents it from being stored in this map |
| * @throws NullPointerException if the specified key or value is null |
| * and this map does not permit null keys or values |
| * @throws IllegalArgumentException if some property of the specified key |
| * or value prevents it from being stored in this map |
| */ |
| V put(K key, V value); |
| |
| /** |
| * Removes the mapping for a key from this map if it is present |
| * (optional operation). More formally, if this map contains a mapping |
| * from key <tt>k</tt> to value <tt>v</tt> such that |
| * <code>(key==null ? k==null : key.equals(k))</code>, that mapping |
| * is removed. (The map can contain at most one such mapping.) |
| * |
| * <p>Returns the value to which this map previously associated the key, |
| * or <tt>null</tt> if the map contained no mapping for the key. |
| * |
| * <p>If this map permits null values, then a return value of |
| * <tt>null</tt> does not <i>necessarily</i> indicate that the map |
| * contained no mapping for the key; it's also possible that the map |
| * explicitly mapped the key to <tt>null</tt>. |
| * |
| * <p>The map will not contain a mapping for the specified key once the |
| * call returns. |
| * |
| * @param key key whose mapping is to be removed from the map |
| * @return the previous value associated with <tt>key</tt>, or |
| * <tt>null</tt> if there was no mapping for <tt>key</tt>. |
| * @throws UnsupportedOperationException if the <tt>remove</tt> operation |
| * is not supported by this map |
| * @throws ClassCastException if the key is of an inappropriate type for |
| * this map |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified key is null and this |
| * map does not permit null keys |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| */ |
| V remove(Object key); |
| |
| |
| // Bulk Operations |
| |
| /** |
| * Copies all of the mappings from the specified map to this map |
| * (optional operation). The effect of this call is equivalent to that |
| * of calling {@link #put(Object,Object) put(k, v)} on this map once |
| * for each mapping from key <tt>k</tt> to value <tt>v</tt> in the |
| * specified map. The behavior of this operation is undefined if the |
| * specified map is modified while the operation is in progress. |
| * |
| * @param m mappings to be stored in this map |
| * @throws UnsupportedOperationException if the <tt>putAll</tt> operation |
| * is not supported by this map |
| * @throws ClassCastException if the class of a key or value in the |
| * specified map prevents it from being stored in this map |
| * @throws NullPointerException if the specified map is null, or if |
| * this map does not permit null keys or values, and the |
| * specified map contains null keys or values |
| * @throws IllegalArgumentException if some property of a key or value in |
| * the specified map prevents it from being stored in this map |
| */ |
| void putAll(Map<? extends K, ? extends V> m); |
| |
| /** |
| * Removes all of the mappings from this map (optional operation). |
| * The map will be empty after this call returns. |
| * |
| * @throws UnsupportedOperationException if the <tt>clear</tt> operation |
| * is not supported by this map |
| */ |
| void clear(); |
| |
| |
| // Views |
| |
| /** |
| * Returns a {@link Set} view of the keys contained in this map. |
| * The set is backed by the map, so changes to the map are |
| * reflected in the set, and vice-versa. If the map is modified |
| * while an iteration over the set is in progress (except through |
| * the iterator's own <tt>remove</tt> operation), the results of |
| * the iteration are undefined. The set supports element removal, |
| * which removes the corresponding mapping from the map, via the |
| * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
| * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
| * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> |
| * operations. |
| * |
| * @return a set view of the keys contained in this map |
| */ |
| Set<K> keySet(); |
| |
| /** |
| * Returns a {@link Collection} view of the values contained in this map. |
| * The collection is backed by the map, so changes to the map are |
| * reflected in the collection, and vice-versa. If the map is |
| * modified while an iteration over the collection is in progress |
| * (except through the iterator's own <tt>remove</tt> operation), |
| * the results of the iteration are undefined. The collection |
| * supports element removal, which removes the corresponding |
| * mapping from the map, via the <tt>Iterator.remove</tt>, |
| * <tt>Collection.remove</tt>, <tt>removeAll</tt>, |
| * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not |
| * support the <tt>add</tt> or <tt>addAll</tt> operations. |
| * |
| * @return a collection view of the values contained in this map |
| */ |
| Collection<V> values(); |
| |
| /** |
| * Returns a {@link Set} view of the mappings contained in this map. |
| * The set is backed by the map, so changes to the map are |
| * reflected in the set, and vice-versa. If the map is modified |
| * while an iteration over the set is in progress (except through |
| * the iterator's own <tt>remove</tt> operation, or through the |
| * <tt>setValue</tt> operation on a map entry returned by the |
| * iterator) the results of the iteration are undefined. The set |
| * supports element removal, which removes the corresponding |
| * mapping from the map, via the <tt>Iterator.remove</tt>, |
| * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and |
| * <tt>clear</tt> operations. It does not support the |
| * <tt>add</tt> or <tt>addAll</tt> operations. |
| * |
| * @return a set view of the mappings contained in this map |
| */ |
| Set<Map.Entry<K, V>> entrySet(); |
| |
| /** |
| * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns |
| * a collection-view of the map, whose elements are of this class. The |
| * <i>only</i> way to obtain a reference to a map entry is from the |
| * iterator of this collection-view. These <tt>Map.Entry</tt> objects are |
| * valid <i>only</i> for the duration of the iteration; more formally, |
| * the behavior of a map entry is undefined if the backing map has been |
| * modified after the entry was returned by the iterator, except through |
| * the <tt>setValue</tt> operation on the map entry. |
| * |
| * @see Map#entrySet() |
| * @since 1.2 |
| */ |
| interface Entry<K,V> { |
| /** |
| * Returns the key corresponding to this entry. |
| * |
| * @return the key corresponding to this entry |
| * @throws IllegalStateException implementations may, but are not |
| * required to, throw this exception if the entry has been |
| * removed from the backing map. |
| */ |
| K getKey(); |
| |
| /** |
| * Returns the value corresponding to this entry. If the mapping |
| * has been removed from the backing map (by the iterator's |
| * <tt>remove</tt> operation), the results of this call are undefined. |
| * |
| * @return the value corresponding to this entry |
| * @throws IllegalStateException implementations may, but are not |
| * required to, throw this exception if the entry has been |
| * removed from the backing map. |
| */ |
| V getValue(); |
| |
| /** |
| * Replaces the value corresponding to this entry with the specified |
| * value (optional operation). (Writes through to the map.) The |
| * behavior of this call is undefined if the mapping has already been |
| * removed from the map (by the iterator's <tt>remove</tt> operation). |
| * |
| * @param value new value to be stored in this entry |
| * @return old value corresponding to the entry |
| * @throws UnsupportedOperationException if the <tt>put</tt> operation |
| * is not supported by the backing map |
| * @throws ClassCastException if the class of the specified value |
| * prevents it from being stored in the backing map |
| * @throws NullPointerException if the backing map does not permit |
| * null values, and the specified value is null |
| * @throws IllegalArgumentException if some property of this value |
| * prevents it from being stored in the backing map |
| * @throws IllegalStateException implementations may, but are not |
| * required to, throw this exception if the entry has been |
| * removed from the backing map. |
| */ |
| 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())) && |
| * (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. |
| * |
| * @param o object to be compared for equality with this map entry |
| * @return <tt>true</tt> if the specified object is equal to this map |
| * entry |
| */ |
| 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>. |
| * |
| * @return the hash code value for this map entry |
| * @see Object#hashCode() |
| * @see Object#equals(Object) |
| * @see #equals(Object) |
| */ |
| int hashCode(); |
| |
| /** |
| * Returns a comparator that compares {@link Map.Entry} in natural order on key. |
| * |
| * <p>The returned comparator is serializable and throws {@link |
| * NullPointerException} when comparing an entry with a null key. |
| * |
| * @param <K> the {@link Comparable} type of then map keys |
| * @param <V> the type of the map values |
| * @return a comparator that compares {@link Map.Entry} in natural order on key. |
| * @see Comparable |
| * @since 1.8 |
| */ |
| 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()); |
| } |
| |
| /** |
| * Returns a comparator that compares {@link Map.Entry} by key using the given |
| * {@link Comparator}. |
| * |
| * <p>The returned comparator is serializable if the specified comparator |
| * is also serializable. |
| * |
| * @param <K> the type of the map keys |
| * @param <V> the type of the map values |
| * @param cmp the key {@link Comparator} |
| * @return a comparator that compares {@link Map.Entry} by the key. |
| * @since 1.8 |
| */ |
| 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()); |
| } |
| } |
| |
| // Comparison and hashing |
| |
| /** |
| * Compares the specified object with this map for equality. Returns |
| * <tt>true</tt> if the given object is also a map and the two maps |
| * represent the same mappings. More formally, two maps <tt>m1</tt> and |
| * <tt>m2</tt> represent the same mappings if |
| * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the |
| * <tt>equals</tt> method works properly across different implementations |
| * of the <tt>Map</tt> interface. |
| * |
| * @param o object to be compared for equality with this map |
| * @return <tt>true</tt> if the specified object is equal to this map |
| */ |
| boolean equals(Object o); |
| |
| /** |
| * Returns the hash code value for this map. The hash code of a map is |
| * defined to be the sum of the hash codes of each entry in the map's |
| * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt> |
| * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps |
| * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of |
| * {@link Object#hashCode}. |
| * |
| * @return the hash code value for this map |
| * @see Map.Entry#hashCode() |
| * @see Object#equals(Object) |
| * @see #equals(Object) |
| */ |
| int hashCode(); |
| |
| /** |
| * Performs the given action for each entry in this map until all entries |
| * have been processed or the action throws an exception. Unless |
| * otherwise specified by the implementing class, actions are performed in |
| * the order of entry set iteration (if an iteration order is specified.) |
| * Exceptions thrown by the action are relayed to the caller. |
| * |
| * @implSpec |
| * The default implementation is equivalent to, for this {@code map}: |
| * <pre> {@code |
| * for (Map.Entry<K, V> entry : map.entrySet()) |
| * action.accept(entry.getKey(), entry.getValue()); |
| * }</pre> |
| * |
| * The default implementation makes no guarantees about synchronization |
| * or atomicity properties of this method. Any implementation providing |
| * atomicity guarantees must override this method and document its |
| * concurrency properties. |
| * |
| * @param action The action to be performed for each entry |
| * @throws NullPointerException if the specified action is null |
| * @throws ConcurrentModificationException if an entry is found to be |
| * removed during iteration |
| * @since 1.8 |
| */ |
| 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); |
| } |
| } |
| } |
