Home » openjdk-7 » java » util » [javadoc | source]

    1   /*
    2    * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.util;
   27   
   28   /**
   29    * The root interface in the <i>collection hierarchy</i>.  A collection
   30    * represents a group of objects, known as its <i>elements</i>.  Some
   31    * collections allow duplicate elements and others do not.  Some are ordered
   32    * and others unordered.  The JDK does not provide any <i>direct</i>
   33    * implementations of this interface: it provides implementations of more
   34    * specific subinterfaces like <tt>Set</tt> and <tt>List</tt>.  This interface
   35    * is typically used to pass collections around and manipulate them where
   36    * maximum generality is desired.
   37    *
   38    * <p><i>Bags</i> or <i>multisets</i> (unordered collections that may contain
   39    * duplicate elements) should implement this interface directly.
   40    *
   41    * <p>All general-purpose <tt>Collection</tt> implementation classes (which
   42    * typically implement <tt>Collection</tt> indirectly through one of its
   43    * subinterfaces) should provide two "standard" constructors: a void (no
   44    * arguments) constructor, which creates an empty collection, and a
   45    * constructor with a single argument of type <tt>Collection</tt>, which
   46    * creates a new collection with the same elements as its argument.  In
   47    * effect, the latter constructor allows the user to copy any collection,
   48    * producing an equivalent collection of the desired implementation type.
   49    * There is no way to enforce this convention (as interfaces cannot contain
   50    * constructors) but all of the general-purpose <tt>Collection</tt>
   51    * implementations in the Java platform libraries comply.
   52    *
   53    * <p>The "destructive" methods contained in this interface, that is, the
   54    * methods that modify the collection on which they operate, are specified to
   55    * throw <tt>UnsupportedOperationException</tt> if this collection does not
   56    * support the operation.  If this is the case, these methods may, but are not
   57    * required to, throw an <tt>UnsupportedOperationException</tt> if the
   58    * invocation would have no effect on the collection.  For example, invoking
   59    * the {@link #addAll(Collection)} method on an unmodifiable collection may,
   60    * but is not required to, throw the exception if the collection to be added
   61    * is empty.
   62    *
   63    * <p><a name="optional-restrictions"/>
   64    * Some collection implementations have restrictions on the elements that
   65    * they may contain.  For example, some implementations prohibit null elements,
   66    * and some have restrictions on the types of their elements.  Attempting to
   67    * add an ineligible element throws an unchecked exception, typically
   68    * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.  Attempting
   69    * to query the presence of an ineligible element may throw an exception,
   70    * or it may simply return false; some implementations will exhibit the former
   71    * behavior and some will exhibit the latter.  More generally, attempting an
   72    * operation on an ineligible element whose completion would not result in
   73    * the insertion of an ineligible element into the collection may throw an
   74    * exception or it may succeed, at the option of the implementation.
   75    * Such exceptions are marked as "optional" in the specification for this
   76    * interface.
   77    *
   78    * <p>It is up to each collection to determine its own synchronization
   79    * policy.  In the absence of a stronger guarantee by the
   80    * implementation, undefined behavior may result from the invocation
   81    * of any method on a collection that is being mutated by another
   82    * thread; this includes direct invocations, passing the collection to
   83    * a method that might perform invocations, and using an existing
   84    * iterator to examine the collection.
   85    *
   86    * <p>Many methods in Collections Framework interfaces are defined in
   87    * terms of the {@link Object#equals(Object) equals} method.  For example,
   88    * the specification for the {@link #contains(Object) contains(Object o)}
   89    * method says: "returns <tt>true</tt> if and only if this collection
   90    * contains at least one element <tt>e</tt> such that
   91    * <tt>(o==null ? e==null : o.equals(e))</tt>."  This specification should
   92    * <i>not</i> be construed to imply that invoking <tt>Collection.contains</tt>
   93    * with a non-null argument <tt>o</tt> will cause <tt>o.equals(e)</tt> to be
   94    * invoked for any element <tt>e</tt>.  Implementations are free to implement
   95    * optimizations whereby the <tt>equals</tt> invocation is avoided, for
   96    * example, by first comparing the hash codes of the two elements.  (The
   97    * {@link Object#hashCode()} specification guarantees that two objects with
   98    * unequal hash codes cannot be equal.)  More generally, implementations of
   99    * the various Collections Framework interfaces are free to take advantage of
  100    * the specified behavior of underlying {@link Object} methods wherever the
  101    * implementor deems it appropriate.
  102    *
  103    * <p>This interface is a member of the
  104    * <a href="{@docRoot}/../technotes/guides/collections/index.html">
  105    * Java Collections Framework</a>.
  106    *
  107    * @param <E> the type of elements in this collection
  108    *
  109    * @author  Josh Bloch
  110    * @author  Neal Gafter
  111    * @see     Set
  112    * @see     List
  113    * @see     Map
  114    * @see     SortedSet
  115    * @see     SortedMap
  116    * @see     HashSet
  117    * @see     TreeSet
  118    * @see     ArrayList
  119    * @see     LinkedList
  120    * @see     Vector
  121    * @see     Collections
  122    * @see     Arrays
  123    * @see     AbstractCollection
  124    * @since 1.2
  125    */
  126   
  127   public interface Collection<E> extends Iterable<E> {
  128       // Query Operations
  129   
  130       /**
  131        * Returns the number of elements in this collection.  If this collection
  132        * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
  133        * <tt>Integer.MAX_VALUE</tt>.
  134        *
  135        * @return the number of elements in this collection
  136        */
  137       int size();
  138   
  139       /**
  140        * Returns <tt>true</tt> if this collection contains no elements.
  141        *
  142        * @return <tt>true</tt> if this collection contains no elements
  143        */
  144       boolean isEmpty();
  145   
  146       /**
  147        * Returns <tt>true</tt> if this collection contains the specified element.
  148        * More formally, returns <tt>true</tt> if and only if this collection
  149        * contains at least one element <tt>e</tt> such that
  150        * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
  151        *
  152        * @param o element whose presence in this collection is to be tested
  153        * @return <tt>true</tt> if this collection contains the specified
  154        *         element
  155        * @throws ClassCastException if the type of the specified element
  156        *         is incompatible with this collection
  157        *         (<a href="#optional-restrictions">optional</a>)
  158        * @throws NullPointerException if the specified element is null and this
  159        *         collection does not permit null elements
  160        *         (<a href="#optional-restrictions">optional</a>)
  161        */
  162       boolean contains(Object o);
  163   
  164       /**
  165        * Returns an iterator over the elements in this collection.  There are no
  166        * guarantees concerning the order in which the elements are returned
  167        * (unless this collection is an instance of some class that provides a
  168        * guarantee).
  169        *
  170        * @return an <tt>Iterator</tt> over the elements in this collection
  171        */
  172       Iterator<E> iterator();
  173   
  174       /**
  175        * Returns an array containing all of the elements in this collection.
  176        * If this collection makes any guarantees as to what order its elements
  177        * are returned by its iterator, this method must return the elements in
  178        * the same order.
  179        *
  180        * <p>The returned array will be "safe" in that no references to it are
  181        * maintained by this collection.  (In other words, this method must
  182        * allocate a new array even if this collection is backed by an array).
  183        * The caller is thus free to modify the returned array.
  184        *
  185        * <p>This method acts as bridge between array-based and collection-based
  186        * APIs.
  187        *
  188        * @return an array containing all of the elements in this collection
  189        */
  190       Object[] toArray();
  191   
  192       /**
  193        * Returns an array containing all of the elements in this collection;
  194        * the runtime type of the returned array is that of the specified array.
  195        * If the collection fits in the specified array, it is returned therein.
  196        * Otherwise, a new array is allocated with the runtime type of the
  197        * specified array and the size of this collection.
  198        *
  199        * <p>If this collection fits in the specified array with room to spare
  200        * (i.e., the array has more elements than this collection), the element
  201        * in the array immediately following the end of the collection is set to
  202        * <tt>null</tt>.  (This is useful in determining the length of this
  203        * collection <i>only</i> if the caller knows that this collection does
  204        * not contain any <tt>null</tt> elements.)
  205        *
  206        * <p>If this collection makes any guarantees as to what order its elements
  207        * are returned by its iterator, this method must return the elements in
  208        * the same order.
  209        *
  210        * <p>Like the {@link #toArray()} method, this method acts as bridge between
  211        * array-based and collection-based APIs.  Further, this method allows
  212        * precise control over the runtime type of the output array, and may,
  213        * under certain circumstances, be used to save allocation costs.
  214        *
  215        * <p>Suppose <tt>x</tt> is a collection known to contain only strings.
  216        * The following code can be used to dump the collection into a newly
  217        * allocated array of <tt>String</tt>:
  218        *
  219        * <pre>
  220        *     String[] y = x.toArray(new String[0]);</pre>
  221        *
  222        * Note that <tt>toArray(new Object[0])</tt> is identical in function to
  223        * <tt>toArray()</tt>.
  224        *
  225        * @param a the array into which the elements of this collection are to be
  226        *        stored, if it is big enough; otherwise, a new array of the same
  227        *        runtime type is allocated for this purpose.
  228        * @return an array containing all of the elements in this collection
  229        * @throws ArrayStoreException if the runtime type of the specified array
  230        *         is not a supertype of the runtime type of every element in
  231        *         this collection
  232        * @throws NullPointerException if the specified array is null
  233        */
  234       <T> T[] toArray(T[] a);
  235   
  236       // Modification Operations
  237   
  238       /**
  239        * Ensures that this collection contains the specified element (optional
  240        * operation).  Returns <tt>true</tt> if this collection changed as a
  241        * result of the call.  (Returns <tt>false</tt> if this collection does
  242        * not permit duplicates and already contains the specified element.)<p>
  243        *
  244        * Collections that support this operation may place limitations on what
  245        * elements may be added to this collection.  In particular, some
  246        * collections will refuse to add <tt>null</tt> elements, and others will
  247        * impose restrictions on the type of elements that may be added.
  248        * Collection classes should clearly specify in their documentation any
  249        * restrictions on what elements may be added.<p>
  250        *
  251        * If a collection refuses to add a particular element for any reason
  252        * other than that it already contains the element, it <i>must</i> throw
  253        * an exception (rather than returning <tt>false</tt>).  This preserves
  254        * the invariant that a collection always contains the specified element
  255        * after this call returns.
  256        *
  257        * @param e element whose presence in this collection is to be ensured
  258        * @return <tt>true</tt> if this collection changed as a result of the
  259        *         call
  260        * @throws UnsupportedOperationException if the <tt>add</tt> operation
  261        *         is not supported by this collection
  262        * @throws ClassCastException if the class of the specified element
  263        *         prevents it from being added to this collection
  264        * @throws NullPointerException if the specified element is null and this
  265        *         collection does not permit null elements
  266        * @throws IllegalArgumentException if some property of the element
  267        *         prevents it from being added to this collection
  268        * @throws IllegalStateException if the element cannot be added at this
  269        *         time due to insertion restrictions
  270        */
  271       boolean add(E e);
  272   
  273       /**
  274        * Removes a single instance of the specified element from this
  275        * collection, if it is present (optional operation).  More formally,
  276        * removes an element <tt>e</tt> such that
  277        * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>, if
  278        * this collection contains one or more such elements.  Returns
  279        * <tt>true</tt> if this collection contained the specified element (or
  280        * equivalently, if this collection changed as a result of the call).
  281        *
  282        * @param o element to be removed from this collection, if present
  283        * @return <tt>true</tt> if an element was removed as a result of this call
  284        * @throws ClassCastException if the type of the specified element
  285        *         is incompatible with this collection
  286        *         (<a href="#optional-restrictions">optional</a>)
  287        * @throws NullPointerException if the specified element is null and this
  288        *         collection does not permit null elements
  289        *         (<a href="#optional-restrictions">optional</a>)
  290        * @throws UnsupportedOperationException if the <tt>remove</tt> operation
  291        *         is not supported by this collection
  292        */
  293       boolean remove(Object o);
  294   
  295   
  296       // Bulk Operations
  297   
  298       /**
  299        * Returns <tt>true</tt> if this collection contains all of the elements
  300        * in the specified collection.
  301        *
  302        * @param  c collection to be checked for containment in this collection
  303        * @return <tt>true</tt> if this collection contains all of the elements
  304        *         in the specified collection
  305        * @throws ClassCastException if the types of one or more elements
  306        *         in the specified collection are incompatible with this
  307        *         collection
  308        *         (<a href="#optional-restrictions">optional</a>)
  309        * @throws NullPointerException if the specified collection contains one
  310        *         or more null elements and this collection does not permit null
  311        *         elements
  312        *         (<a href="#optional-restrictions">optional</a>),
  313        *         or if the specified collection is null.
  314        * @see    #contains(Object)
  315        */
  316       boolean containsAll(Collection<?> c);
  317   
  318       /**
  319        * Adds all of the elements in the specified collection to this collection
  320        * (optional operation).  The behavior of this operation is undefined if
  321        * the specified collection is modified while the operation is in progress.
  322        * (This implies that the behavior of this call is undefined if the
  323        * specified collection is this collection, and this collection is
  324        * nonempty.)
  325        *
  326        * @param c collection containing elements to be added to this collection
  327        * @return <tt>true</tt> if this collection changed as a result of the call
  328        * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
  329        *         is not supported by this collection
  330        * @throws ClassCastException if the class of an element of the specified
  331        *         collection prevents it from being added to this collection
  332        * @throws NullPointerException if the specified collection contains a
  333        *         null element and this collection does not permit null elements,
  334        *         or if the specified collection is null
  335        * @throws IllegalArgumentException if some property of an element of the
  336        *         specified collection prevents it from being added to this
  337        *         collection
  338        * @throws IllegalStateException if not all the elements can be added at
  339        *         this time due to insertion restrictions
  340        * @see #add(Object)
  341        */
  342       boolean addAll(Collection<? extends E> c);
  343   
  344       /**
  345        * Removes all of this collection's elements that are also contained in the
  346        * specified collection (optional operation).  After this call returns,
  347        * this collection will contain no elements in common with the specified
  348        * collection.
  349        *
  350        * @param c collection containing elements to be removed from this collection
  351        * @return <tt>true</tt> if this collection changed as a result of the
  352        *         call
  353        * @throws UnsupportedOperationException if the <tt>removeAll</tt> method
  354        *         is not supported by this collection
  355        * @throws ClassCastException if the types of one or more elements
  356        *         in this collection are incompatible with the specified
  357        *         collection
  358        *         (<a href="#optional-restrictions">optional</a>)
  359        * @throws NullPointerException if this collection contains one or more
  360        *         null elements and the specified collection does not support
  361        *         null elements
  362        *         (<a href="#optional-restrictions">optional</a>),
  363        *         or if the specified collection is null
  364        * @see #remove(Object)
  365        * @see #contains(Object)
  366        */
  367       boolean removeAll(Collection<?> c);
  368   
  369       /**
  370        * Retains only the elements in this collection that are contained in the
  371        * specified collection (optional operation).  In other words, removes from
  372        * this collection all of its elements that are not contained in the
  373        * specified collection.
  374        *
  375        * @param c collection containing elements to be retained in this collection
  376        * @return <tt>true</tt> if this collection changed as a result of the call
  377        * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
  378        *         is not supported by this collection
  379        * @throws ClassCastException if the types of one or more elements
  380        *         in this collection are incompatible with the specified
  381        *         collection
  382        *         (<a href="#optional-restrictions">optional</a>)
  383        * @throws NullPointerException if this collection contains one or more
  384        *         null elements and the specified collection does not permit null
  385        *         elements
  386        *         (<a href="#optional-restrictions">optional</a>),
  387        *         or if the specified collection is null
  388        * @see #remove(Object)
  389        * @see #contains(Object)
  390        */
  391       boolean retainAll(Collection<?> c);
  392   
  393       /**
  394        * Removes all of the elements from this collection (optional operation).
  395        * The collection will be empty after this method returns.
  396        *
  397        * @throws UnsupportedOperationException if the <tt>clear</tt> operation
  398        *         is not supported by this collection
  399        */
  400       void clear();
  401   
  402   
  403       // Comparison and hashing
  404   
  405       /**
  406        * Compares the specified object with this collection for equality. <p>
  407        *
  408        * While the <tt>Collection</tt> interface adds no stipulations to the
  409        * general contract for the <tt>Object.equals</tt>, programmers who
  410        * implement the <tt>Collection</tt> interface "directly" (in other words,
  411        * create a class that is a <tt>Collection</tt> but is not a <tt>Set</tt>
  412        * or a <tt>List</tt>) must exercise care if they choose to override the
  413        * <tt>Object.equals</tt>.  It is not necessary to do so, and the simplest
  414        * course of action is to rely on <tt>Object</tt>'s implementation, but
  415        * the implementor may wish to implement a "value comparison" in place of
  416        * the default "reference comparison."  (The <tt>List</tt> and
  417        * <tt>Set</tt> interfaces mandate such value comparisons.)<p>
  418        *
  419        * The general contract for the <tt>Object.equals</tt> method states that
  420        * equals must be symmetric (in other words, <tt>a.equals(b)</tt> if and
  421        * only if <tt>b.equals(a)</tt>).  The contracts for <tt>List.equals</tt>
  422        * and <tt>Set.equals</tt> state that lists are only equal to other lists,
  423        * and sets to other sets.  Thus, a custom <tt>equals</tt> method for a
  424        * collection class that implements neither the <tt>List</tt> nor
  425        * <tt>Set</tt> interface must return <tt>false</tt> when this collection
  426        * is compared to any list or set.  (By the same logic, it is not possible
  427        * to write a class that correctly implements both the <tt>Set</tt> and
  428        * <tt>List</tt> interfaces.)
  429        *
  430        * @param o object to be compared for equality with this collection
  431        * @return <tt>true</tt> if the specified object is equal to this
  432        * collection
  433        *
  434        * @see Object#equals(Object)
  435        * @see Set#equals(Object)
  436        * @see List#equals(Object)
  437        */
  438       boolean equals(Object o);
  439   
  440       /**
  441        * Returns the hash code value for this collection.  While the
  442        * <tt>Collection</tt> interface adds no stipulations to the general
  443        * contract for the <tt>Object.hashCode</tt> method, programmers should
  444        * take note that any class that overrides the <tt>Object.equals</tt>
  445        * method must also override the <tt>Object.hashCode</tt> method in order
  446        * to satisfy the general contract for the <tt>Object.hashCode</tt> method.
  447        * In particular, <tt>c1.equals(c2)</tt> implies that
  448        * <tt>c1.hashCode()==c2.hashCode()</tt>.
  449        *
  450        * @return the hash code value for this collection
  451        *
  452        * @see Object#hashCode()
  453        * @see Object#equals(Object)
  454        */
  455       int hashCode();
  456   }

Home » openjdk-7 » java » util » [javadoc | source]