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/* |
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* Copyright (c) 1997, 2006, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Sun designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Sun in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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|
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package java.util; |
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|
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/** |
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* The root interface in the <i>collection hierarchy</i>. A collection |
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* represents a group of objects, known as its <i>elements</i>. Some |
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* collections allow duplicate elements and others do not. Some are ordered |
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* and others unordered. The JDK does not provide any <i>direct</i> |
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* implementations of this interface: it provides implementations of more |
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* specific subinterfaces like <tt>Set</tt> and <tt>List</tt>. This interface |
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* is typically used to pass collections around and manipulate them where |
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* maximum generality is desired. |
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* |
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* <p><i>Bags</i> or <i>multisets</i> (unordered collections that may contain |
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* duplicate elements) should implement this interface directly. |
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* |
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* <p>All general-purpose <tt>Collection</tt> implementation classes (which |
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* typically implement <tt>Collection</tt> indirectly through one of its |
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* subinterfaces) should provide two "standard" constructors: a void (no |
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* arguments) constructor, which creates an empty collection, and a |
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* constructor with a single argument of type <tt>Collection</tt>, which |
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* creates a new collection with the same elements as its argument. In |
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* effect, the latter constructor allows the user to copy any collection, |
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* producing an equivalent collection of the desired implementation type. |
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* There is no way to enforce this convention (as interfaces cannot contain |
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* constructors) but all of the general-purpose <tt>Collection</tt> |
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* implementations in the Java platform libraries comply. |
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* |
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* <p>The "destructive" methods contained in this interface, that is, the |
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* methods that modify the collection on which they operate, are specified to |
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* throw <tt>UnsupportedOperationException</tt> if this collection does not |
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* support the operation. If this is the case, these methods may, but are not |
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* required to, throw an <tt>UnsupportedOperationException</tt> if the |
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* invocation would have no effect on the collection. For example, invoking |
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* the {@link #addAll(Collection)} method on an unmodifiable collection may, |
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* but is not required to, throw the exception if the collection to be added |
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* is empty. |
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* |
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* <p>Some collection implementations have restrictions on the elements that |
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* they may contain. For example, some implementations prohibit null elements, |
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* and some have restrictions on the types of their elements. Attempting to |
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* add an ineligible element throws an unchecked exception, typically |
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* <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting |
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* to query the presence of an ineligible element may throw an exception, |
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* or it may simply return false; some implementations will exhibit the former |
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* behavior and some will exhibit the latter. More generally, attempting an |
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* operation on an ineligible element whose completion would not result in |
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* the insertion of an ineligible element into the collection may throw an |
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* exception or it may succeed, at the option of the implementation. |
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* Such exceptions are marked as "optional" in the specification for this |
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* interface. |
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* |
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* <p>It is up to each collection to determine its own synchronization |
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* policy. In the absence of a stronger guarantee by the |
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* implementation, undefined behavior may result from the invocation |
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* of any method on a collection that is being mutated by another |
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* thread; this includes direct invocations, passing the collection to |
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* a method that might perform invocations, and using an existing |
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* iterator to examine the collection. |
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* |
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* <p>Many methods in Collections Framework interfaces are defined in |
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* terms of the {@link Object#equals(Object) equals} method. For example, |
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* the specification for the {@link #contains(Object) contains(Object o)} |
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* method says: "returns <tt>true</tt> if and only if this collection |
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* contains at least one element <tt>e</tt> such that |
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* <tt>(o==null ? e==null : o.equals(e))</tt>." This specification should |
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* <i>not</i> be construed to imply that invoking <tt>Collection.contains</tt> |
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* with a non-null argument <tt>o</tt> will cause <tt>o.equals(e)</tt> to be |
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* invoked for any element <tt>e</tt>. Implementations are free to implement |
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* optimizations whereby the <tt>equals</tt> invocation is avoided, for |
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* example, by first comparing the hash codes of the two elements. (The |
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* {@link Object#hashCode()} specification guarantees that two objects with |
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* unequal hash codes cannot be equal.) More generally, implementations of |
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* the various Collections Framework interfaces are free to take advantage of |
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* the specified behavior of underlying {@link Object} methods wherever the |
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* implementor deems it appropriate. |
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* |
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* <p>This interface is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @author Josh Bloch |
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* @author Neal Gafter |
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* @see Set |
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* @see List |
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* @see Map |
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* @see SortedSet |
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* @see SortedMap |
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* @see HashSet |
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* @see TreeSet |
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* @see ArrayList |
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* @see LinkedList |
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* @see Vector |
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* @see Collections |
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* @see Arrays |
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* @see AbstractCollection |
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* @since 1.2 |
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*/ |
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|
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public interface Collection<E> extends Iterable<E> { |
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// Query Operations |
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|
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/** |
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* Returns the number of elements in this collection. If this collection |
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* contains more than <tt>Integer.MAX_VALUE</tt> elements, returns |
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* <tt>Integer.MAX_VALUE</tt>. |
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* |
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* @return the number of elements in this collection |
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*/ |
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int size(); |
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|
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/** |
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* Returns <tt>true</tt> if this collection contains no elements. |
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* |
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* @return <tt>true</tt> if this collection contains no elements |
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*/ |
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boolean isEmpty(); |
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|
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/** |
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* Returns <tt>true</tt> if this collection contains the specified element. |
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* More formally, returns <tt>true</tt> if and only if this collection |
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* contains at least one element <tt>e</tt> such that |
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* <tt>(o==null ? e==null : o.equals(e))</tt>. |
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* |
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* @param o element whose presence in this collection is to be tested |
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* @return <tt>true</tt> if this collection contains the specified |
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* element |
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* @throws ClassCastException if the type of the specified element |
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* is incompatible with this collection (optional) |
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* @throws NullPointerException if the specified element is null and this |
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* collection does not permit null elements (optional) |
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*/ |
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boolean contains(Object o); |
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|
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/** |
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* Returns an iterator over the elements in this collection. There are no |
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* guarantees concerning the order in which the elements are returned |
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* (unless this collection is an instance of some class that provides a |
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* guarantee). |
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* |
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* @return an <tt>Iterator</tt> over the elements in this collection |
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*/ |
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Iterator<E> iterator(); |
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|
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/** |
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* Returns an array containing all of the elements in this collection. |
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* If this collection makes any guarantees as to what order its elements |
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* are returned by its iterator, this method must return the elements in |
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* the same order. |
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* |
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* <p>The returned array will be "safe" in that no references to it are |
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* maintained by this collection. (In other words, this method must |
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* allocate a new array even if this collection is backed by an array). |
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* The caller is thus free to modify the returned array. |
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* |
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* <p>This method acts as bridge between array-based and collection-based |
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* APIs. |
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* |
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* @return an array containing all of the elements in this collection |
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*/ |
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Object[] toArray(); |
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|
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/** |
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* Returns an array containing all of the elements in this collection; |
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* the runtime type of the returned array is that of the specified array. |
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* If the collection fits in the specified array, it is returned therein. |
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* Otherwise, a new array is allocated with the runtime type of the |
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* specified array and the size of this collection. |
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* |
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* <p>If this collection fits in the specified array with room to spare |
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* (i.e., the array has more elements than this collection), the element |
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* in the array immediately following the end of the collection is set to |
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* <tt>null</tt>. (This is useful in determining the length of this |
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* collection <i>only</i> if the caller knows that this collection does |
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* not contain any <tt>null</tt> elements.) |
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* |
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* <p>If this collection makes any guarantees as to what order its elements |
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* are returned by its iterator, this method must return the elements in |
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* the same order. |
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* |
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* <p>Like the {@link #toArray()} method, this method acts as bridge between |
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* array-based and collection-based APIs. Further, this method allows |
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* precise control over the runtime type of the output array, and may, |
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* under certain circumstances, be used to save allocation costs. |
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* |
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* <p>Suppose <tt>x</tt> is a collection known to contain only strings. |
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* The following code can be used to dump the collection into a newly |
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* allocated array of <tt>String</tt>: |
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* |
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* <pre> |
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* String[] y = x.toArray(new String[0]);</pre> |
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* |
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* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
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* <tt>toArray()</tt>. |
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* |
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* @param a the array into which the elements of this collection are to be |
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* stored, if it is big enough; otherwise, a new array of the same |
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* runtime type is allocated for this purpose. |
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* @return an array containing all of the elements in this collection |
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* @throws ArrayStoreException if the runtime type of the specified array |
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* is not a supertype of the runtime type of every element in |
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* this collection |
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* @throws NullPointerException if the specified array is null |
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*/ |
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<T> T[] toArray(T[] a); |
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|
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// Modification Operations |
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|
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/** |
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* Ensures that this collection contains the specified element (optional |
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* operation). Returns <tt>true</tt> if this collection changed as a |
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* result of the call. (Returns <tt>false</tt> if this collection does |
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* not permit duplicates and already contains the specified element.)<p> |
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* |
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* Collections that support this operation may place limitations on what |
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* elements may be added to this collection. In particular, some |
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* collections will refuse to add <tt>null</tt> elements, and others will |
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* impose restrictions on the type of elements that may be added. |
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* Collection classes should clearly specify in their documentation any |
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* restrictions on what elements may be added.<p> |
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* |
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* If a collection refuses to add a particular element for any reason |
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* other than that it already contains the element, it <i>must</i> throw |
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* an exception (rather than returning <tt>false</tt>). This preserves |
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* the invariant that a collection always contains the specified element |
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* after this call returns. |
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* |
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* @param e element whose presence in this collection is to be ensured |
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* @return <tt>true</tt> if this collection changed as a result of the |
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* call |
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* @throws UnsupportedOperationException if the <tt>add</tt> operation |
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* is not supported by this collection |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this collection |
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* @throws NullPointerException if the specified element is null and this |
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* collection does not permit null elements |
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* @throws IllegalArgumentException if some property of the element |
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* prevents it from being added to this collection |
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* @throws IllegalStateException if the element cannot be added at this |
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* time due to insertion restrictions |
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*/ |
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boolean add(E e); |
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|
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/** |
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* Removes a single instance of the specified element from this |
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* collection, if it is present (optional operation). More formally, |
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* removes an element <tt>e</tt> such that |
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* <tt>(o==null ? e==null : o.equals(e))</tt>, if |
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* this collection contains one or more such elements. Returns |
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* <tt>true</tt> if this collection contained the specified element (or |
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* equivalently, if this collection changed as a result of the call). |
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* |
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* @param o element to be removed from this collection, if present |
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* @return <tt>true</tt> if an element was removed as a result of this call |
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* @throws ClassCastException if the type of the specified element |
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* is incompatible with this collection (optional) |
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* @throws NullPointerException if the specified element is null and this |
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* collection does not permit null elements (optional) |
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* @throws UnsupportedOperationException if the <tt>remove</tt> operation |
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* is not supported by this collection |
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*/ |
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boolean remove(Object o); |
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|
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|
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// Bulk Operations |
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|
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/** |
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* Returns <tt>true</tt> if this collection contains all of the elements |
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* in the specified collection. |
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* |
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* @param c collection to be checked for containment in this collection |
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* @return <tt>true</tt> if this collection contains all of the elements |
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* in the specified collection |
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* @throws ClassCastException if the types of one or more elements |
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* in the specified collection are incompatible with this |
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* collection (optional) |
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* @throws NullPointerException if the specified collection contains one |
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* or more null elements and this collection does not permit null |
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* elements (optional), or if the specified collection is null |
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* @see #contains(Object) |
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*/ |
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boolean containsAll(Collection<?> c); |
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|
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/** |
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* Adds all of the elements in the specified collection to this collection |
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* (optional operation). The behavior of this operation is undefined if |
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* the specified collection is modified while the operation is in progress. |
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* (This implies that the behavior of this call is undefined if the |
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* specified collection is this collection, and this collection is |
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* nonempty.) |
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* |
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* @param c collection containing elements to be added to this collection |
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* @return <tt>true</tt> if this collection changed as a result of the call |
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* @throws UnsupportedOperationException if the <tt>addAll</tt> operation |
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* is not supported by this collection |
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* @throws ClassCastException if the class of an element of the specified |
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* collection prevents it from being added to this collection |
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* @throws NullPointerException if the specified collection contains a |
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* null element and this collection does not permit null elements, |
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* or if the specified collection is null |
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* @throws IllegalArgumentException if some property of an element of the |
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* specified collection prevents it from being added to this |
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* collection |
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* @throws IllegalStateException if not all the elements can be added at |
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* this time due to insertion restrictions |
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* @see #add(Object) |
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*/ |
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boolean addAll(Collection<? extends E> c); |
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|
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/** |
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* Removes all of this collection's elements that are also contained in the |
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* specified collection (optional operation). After this call returns, |
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* this collection will contain no elements in common with the specified |
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* collection. |
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* |
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* @param c collection containing elements to be removed from this collection |
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* @return <tt>true</tt> if this collection changed as a result of the |
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* call |
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* @throws UnsupportedOperationException if the <tt>removeAll</tt> method |
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* is not supported by this collection |
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* @throws ClassCastException if the types of one or more elements |
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* in this collection are incompatible with the specified |
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* collection (optional) |
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* @throws NullPointerException if this collection contains one or more |
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* null elements and the specified collection does not support |
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* null elements (optional), or if the specified collection is null |
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* @see #remove(Object) |
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* @see #contains(Object) |
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*/ |
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boolean removeAll(Collection<?> c); |
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|
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/** |
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* Retains only the elements in this collection that are contained in the |
| 358 |
* specified collection (optional operation). In other words, removes from |
| 359 |
* this collection all of its elements that are not contained in the |
| 360 |
* specified collection. |
| 361 |
* |
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* @param c collection containing elements to be retained in this collection |
| 363 |
* @return <tt>true</tt> if this collection changed as a result of the call |
| 364 |
* @throws UnsupportedOperationException if the <tt>retainAll</tt> operation |
| 365 |
* is not supported by this collection |
| 366 |
* @throws ClassCastException if the types of one or more elements |
| 367 |
* in this collection are incompatible with the specified |
| 368 |
* collection (optional) |
| 369 |
* @throws NullPointerException if this collection contains one or more |
| 370 |
* null elements and the specified collection does not permit null |
| 371 |
* elements (optional), or if the specified collection is null |
| 372 |
* @see #remove(Object) |
| 373 |
* @see #contains(Object) |
| 374 |
*/ |
| 375 |
boolean retainAll(Collection<?> c); |
| 376 |
|
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/** |
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* Removes all of the elements from this collection (optional operation). |
| 379 |
* The collection will be empty after this method returns. |
| 380 |
* |
| 381 |
* @throws UnsupportedOperationException if the <tt>clear</tt> operation |
| 382 |
* is not supported by this collection |
| 383 |
*/ |
| 384 |
void clear(); |
| 385 |
|
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|
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// Comparison and hashing |
| 388 |
|
| 389 |
/** |
| 390 |
* Compares the specified object with this collection for equality. <p> |
| 391 |
* |
| 392 |
* While the <tt>Collection</tt> interface adds no stipulations to the |
| 393 |
* general contract for the <tt>Object.equals</tt>, programmers who |
| 394 |
* implement the <tt>Collection</tt> interface "directly" (in other words, |
| 395 |
* create a class that is a <tt>Collection</tt> but is not a <tt>Set</tt> |
| 396 |
* or a <tt>List</tt>) must exercise care if they choose to override the |
| 397 |
* <tt>Object.equals</tt>. It is not necessary to do so, and the simplest |
| 398 |
* course of action is to rely on <tt>Object</tt>'s implementation, but |
| 399 |
* the implementor may wish to implement a "value comparison" in place of |
| 400 |
* the default "reference comparison." (The <tt>List</tt> and |
| 401 |
* <tt>Set</tt> interfaces mandate such value comparisons.)<p> |
| 402 |
* |
| 403 |
* The general contract for the <tt>Object.equals</tt> method states that |
| 404 |
* equals must be symmetric (in other words, <tt>a.equals(b)</tt> if and |
| 405 |
* only if <tt>b.equals(a)</tt>). The contracts for <tt>List.equals</tt> |
| 406 |
* and <tt>Set.equals</tt> state that lists are only equal to other lists, |
| 407 |
* and sets to other sets. Thus, a custom <tt>equals</tt> method for a |
| 408 |
* collection class that implements neither the <tt>List</tt> nor |
| 409 |
* <tt>Set</tt> interface must return <tt>false</tt> when this collection |
| 410 |
* is compared to any list or set. (By the same logic, it is not possible |
| 411 |
* to write a class that correctly implements both the <tt>Set</tt> and |
| 412 |
* <tt>List</tt> interfaces.) |
| 413 |
* |
| 414 |
* @param o object to be compared for equality with this collection |
| 415 |
* @return <tt>true</tt> if the specified object is equal to this |
| 416 |
* collection |
| 417 |
* |
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* @see Object#equals(Object) |
| 419 |
* @see Set#equals(Object) |
| 420 |
* @see List#equals(Object) |
| 421 |
*/ |
| 422 |
boolean equals(Object o); |
| 423 |
|
| 424 |
/** |
| 425 |
* Returns the hash code value for this collection. While the |
| 426 |
* <tt>Collection</tt> interface adds no stipulations to the general |
| 427 |
* contract for the <tt>Object.hashCode</tt> method, programmers should |
| 428 |
* take note that any class that overrides the <tt>Object.equals</tt> |
| 429 |
* method must also override the <tt>Object.hashCode</tt> method in order |
| 430 |
* to satisfy the general contract for the <tt>Object.hashCode</tt> method. |
| 431 |
* In particular, <tt>c1.equals(c2)</tt> implies that |
| 432 |
* <tt>c1.hashCode()==c2.hashCode()</tt>. |
| 433 |
* |
| 434 |
* @return the hash code value for this collection |
| 435 |
* |
| 436 |
* @see Object#hashCode() |
| 437 |
* @see Object#equals(Object) |
| 438 |
*/ |
| 439 |
int hashCode(); |
| 440 |
} |
