jaroslav@557: /* jaroslav@557: * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved. jaroslav@557: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. jaroslav@557: * jaroslav@557: * This code is free software; you can redistribute it and/or modify it jaroslav@557: * under the terms of the GNU General Public License version 2 only, as jaroslav@557: * published by the Free Software Foundation. Oracle designates this jaroslav@557: * particular file as subject to the "Classpath" exception as provided jaroslav@557: * by Oracle in the LICENSE file that accompanied this code. jaroslav@557: * jaroslav@557: * This code is distributed in the hope that it will be useful, but WITHOUT jaroslav@557: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or jaroslav@557: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License jaroslav@557: * version 2 for more details (a copy is included in the LICENSE file that jaroslav@557: * accompanied this code). jaroslav@557: * jaroslav@557: * You should have received a copy of the GNU General Public License version jaroslav@557: * 2 along with this work; if not, write to the Free Software Foundation, jaroslav@557: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. jaroslav@557: * jaroslav@557: * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA jaroslav@557: * or visit www.oracle.com if you need additional information or have any jaroslav@557: * questions. jaroslav@557: */ jaroslav@557: jaroslav@557: package java.util; jaroslav@557: jaroslav@557: /** jaroslav@557: * The root interface in the collection hierarchy. A collection jaroslav@557: * represents a group of objects, known as its elements. Some jaroslav@557: * collections allow duplicate elements and others do not. Some are ordered jaroslav@557: * and others unordered. The JDK does not provide any direct jaroslav@557: * implementations of this interface: it provides implementations of more jaroslav@557: * specific subinterfaces like Set and List. This interface jaroslav@557: * is typically used to pass collections around and manipulate them where jaroslav@557: * maximum generality is desired. jaroslav@557: * jaroslav@557: *

Bags or multisets (unordered collections that may contain jaroslav@557: * duplicate elements) should implement this interface directly. jaroslav@557: * jaroslav@557: *

All general-purpose Collection implementation classes (which jaroslav@557: * typically implement Collection indirectly through one of its jaroslav@557: * subinterfaces) should provide two "standard" constructors: a void (no jaroslav@557: * arguments) constructor, which creates an empty collection, and a jaroslav@557: * constructor with a single argument of type Collection, which jaroslav@557: * creates a new collection with the same elements as its argument. In jaroslav@557: * effect, the latter constructor allows the user to copy any collection, jaroslav@557: * producing an equivalent collection of the desired implementation type. jaroslav@557: * There is no way to enforce this convention (as interfaces cannot contain jaroslav@557: * constructors) but all of the general-purpose Collection jaroslav@557: * implementations in the Java platform libraries comply. jaroslav@557: * jaroslav@557: *

The "destructive" methods contained in this interface, that is, the jaroslav@557: * methods that modify the collection on which they operate, are specified to jaroslav@557: * throw UnsupportedOperationException if this collection does not jaroslav@557: * support the operation. If this is the case, these methods may, but are not jaroslav@557: * required to, throw an UnsupportedOperationException if the jaroslav@557: * invocation would have no effect on the collection. For example, invoking jaroslav@557: * the {@link #addAll(Collection)} method on an unmodifiable collection may, jaroslav@557: * but is not required to, throw the exception if the collection to be added jaroslav@557: * is empty. jaroslav@557: * jaroslav@557: *

jaroslav@557: * Some collection implementations have restrictions on the elements that jaroslav@557: * they may contain. For example, some implementations prohibit null elements, jaroslav@557: * and some have restrictions on the types of their elements. Attempting to jaroslav@557: * add an ineligible element throws an unchecked exception, typically jaroslav@557: * NullPointerException or ClassCastException. Attempting jaroslav@557: * to query the presence of an ineligible element may throw an exception, jaroslav@557: * or it may simply return false; some implementations will exhibit the former jaroslav@557: * behavior and some will exhibit the latter. More generally, attempting an jaroslav@557: * operation on an ineligible element whose completion would not result in jaroslav@557: * the insertion of an ineligible element into the collection may throw an jaroslav@557: * exception or it may succeed, at the option of the implementation. jaroslav@557: * Such exceptions are marked as "optional" in the specification for this jaroslav@557: * interface. jaroslav@557: * jaroslav@557: *

It is up to each collection to determine its own synchronization jaroslav@557: * policy. In the absence of a stronger guarantee by the jaroslav@557: * implementation, undefined behavior may result from the invocation jaroslav@557: * of any method on a collection that is being mutated by another jaroslav@557: * thread; this includes direct invocations, passing the collection to jaroslav@557: * a method that might perform invocations, and using an existing jaroslav@557: * iterator to examine the collection. jaroslav@557: * jaroslav@557: *

Many methods in Collections Framework interfaces are defined in jaroslav@557: * terms of the {@link Object#equals(Object) equals} method. For example, jaroslav@557: * the specification for the {@link #contains(Object) contains(Object o)} jaroslav@557: * method says: "returns true if and only if this collection jaroslav@557: * contains at least one element e such that jaroslav@557: * (o==null ? e==null : o.equals(e))." This specification should jaroslav@557: * not be construed to imply that invoking Collection.contains jaroslav@557: * with a non-null argument o will cause o.equals(e) to be jaroslav@557: * invoked for any element e. Implementations are free to implement jaroslav@557: * optimizations whereby the equals invocation is avoided, for jaroslav@557: * example, by first comparing the hash codes of the two elements. (The jaroslav@557: * {@link Object#hashCode()} specification guarantees that two objects with jaroslav@557: * unequal hash codes cannot be equal.) More generally, implementations of jaroslav@557: * the various Collections Framework interfaces are free to take advantage of jaroslav@557: * the specified behavior of underlying {@link Object} methods wherever the jaroslav@557: * implementor deems it appropriate. jaroslav@557: * jaroslav@557: *

This interface is a member of the jaroslav@557: * jaroslav@557: * Java Collections Framework. jaroslav@557: * jaroslav@557: * @param the type of elements in this collection jaroslav@557: * jaroslav@557: * @author Josh Bloch jaroslav@557: * @author Neal Gafter jaroslav@557: * @see Set jaroslav@557: * @see List jaroslav@557: * @see Map jaroslav@557: * @see SortedSet jaroslav@557: * @see SortedMap jaroslav@557: * @see HashSet jaroslav@557: * @see TreeSet jaroslav@557: * @see ArrayList jaroslav@557: * @see LinkedList jaroslav@557: * @see Vector jaroslav@557: * @see Collections jaroslav@557: * @see Arrays jaroslav@557: * @see AbstractCollection jaroslav@557: * @since 1.2 jaroslav@557: */ jaroslav@557: jaroslav@557: public interface Collection extends Iterable { jaroslav@557: // Query Operations jaroslav@557: jaroslav@557: /** jaroslav@557: * Returns the number of elements in this collection. If this collection jaroslav@557: * contains more than Integer.MAX_VALUE elements, returns jaroslav@557: * Integer.MAX_VALUE. jaroslav@557: * jaroslav@557: * @return the number of elements in this collection jaroslav@557: */ jaroslav@557: int size(); jaroslav@557: jaroslav@557: /** jaroslav@557: * Returns true if this collection contains no elements. jaroslav@557: * jaroslav@557: * @return true if this collection contains no elements jaroslav@557: */ jaroslav@557: boolean isEmpty(); jaroslav@557: jaroslav@557: /** jaroslav@557: * Returns true if this collection contains the specified element. jaroslav@557: * More formally, returns true if and only if this collection jaroslav@557: * contains at least one element e such that jaroslav@557: * (o==null ? e==null : o.equals(e)). jaroslav@557: * jaroslav@557: * @param o element whose presence in this collection is to be tested jaroslav@557: * @return true if this collection contains the specified jaroslav@557: * element jaroslav@557: * @throws ClassCastException if the type of the specified element jaroslav@557: * is incompatible with this collection jaroslav@557: * (optional) jaroslav@557: * @throws NullPointerException if the specified element is null and this jaroslav@557: * collection does not permit null elements jaroslav@557: * (optional) jaroslav@557: */ jaroslav@557: boolean contains(Object o); jaroslav@557: jaroslav@557: /** jaroslav@557: * Returns an iterator over the elements in this collection. There are no jaroslav@557: * guarantees concerning the order in which the elements are returned jaroslav@557: * (unless this collection is an instance of some class that provides a jaroslav@557: * guarantee). jaroslav@557: * jaroslav@557: * @return an Iterator over the elements in this collection jaroslav@557: */ jaroslav@557: Iterator iterator(); jaroslav@557: jaroslav@557: /** jaroslav@557: * Returns an array containing all of the elements in this collection. jaroslav@557: * If this collection makes any guarantees as to what order its elements jaroslav@557: * are returned by its iterator, this method must return the elements in jaroslav@557: * the same order. jaroslav@557: * jaroslav@557: *

The returned array will be "safe" in that no references to it are jaroslav@557: * maintained by this collection. (In other words, this method must jaroslav@557: * allocate a new array even if this collection is backed by an array). jaroslav@557: * The caller is thus free to modify the returned array. jaroslav@557: * jaroslav@557: *

This method acts as bridge between array-based and collection-based jaroslav@557: * APIs. jaroslav@557: * jaroslav@557: * @return an array containing all of the elements in this collection jaroslav@557: */ jaroslav@557: Object[] toArray(); jaroslav@557: jaroslav@557: /** jaroslav@557: * Returns an array containing all of the elements in this collection; jaroslav@557: * the runtime type of the returned array is that of the specified array. jaroslav@557: * If the collection fits in the specified array, it is returned therein. jaroslav@557: * Otherwise, a new array is allocated with the runtime type of the jaroslav@557: * specified array and the size of this collection. jaroslav@557: * jaroslav@557: *

If this collection fits in the specified array with room to spare jaroslav@557: * (i.e., the array has more elements than this collection), the element jaroslav@557: * in the array immediately following the end of the collection is set to jaroslav@557: * null. (This is useful in determining the length of this jaroslav@557: * collection only if the caller knows that this collection does jaroslav@557: * not contain any null elements.) jaroslav@557: * jaroslav@557: *

If this collection makes any guarantees as to what order its elements jaroslav@557: * are returned by its iterator, this method must return the elements in jaroslav@557: * the same order. jaroslav@557: * jaroslav@557: *

Like the {@link #toArray()} method, this method acts as bridge between jaroslav@557: * array-based and collection-based APIs. Further, this method allows jaroslav@557: * precise control over the runtime type of the output array, and may, jaroslav@557: * under certain circumstances, be used to save allocation costs. jaroslav@557: * jaroslav@557: *

Suppose x is a collection known to contain only strings. jaroslav@557: * The following code can be used to dump the collection into a newly jaroslav@557: * allocated array of String: jaroslav@557: * jaroslav@557: * 

jaroslav@557:      *     String[] y = x.toArray(new String[0]);
jaroslav@557: * jaroslav@557: * Note that toArray(new Object[0]) is identical in function to jaroslav@557: * toArray(). jaroslav@557: * jaroslav@557: * @param a the array into which the elements of this collection are to be jaroslav@557: * stored, if it is big enough; otherwise, a new array of the same jaroslav@557: * runtime type is allocated for this purpose. jaroslav@557: * @return an array containing all of the elements in this collection jaroslav@557: * @throws ArrayStoreException if the runtime type of the specified array jaroslav@557: * is not a supertype of the runtime type of every element in jaroslav@557: * this collection jaroslav@557: * @throws NullPointerException if the specified array is null jaroslav@557: */ jaroslav@557: T[] toArray(T[] a); jaroslav@557: jaroslav@557: // Modification Operations jaroslav@557: jaroslav@557: /** jaroslav@557: * Ensures that this collection contains the specified element (optional jaroslav@557: * operation). Returns true if this collection changed as a jaroslav@557: * result of the call. (Returns false if this collection does jaroslav@557: * not permit duplicates and already contains the specified element.)

jaroslav@557: * jaroslav@557: * Collections that support this operation may place limitations on what jaroslav@557: * elements may be added to this collection. In particular, some jaroslav@557: * collections will refuse to add null elements, and others will jaroslav@557: * impose restrictions on the type of elements that may be added. jaroslav@557: * Collection classes should clearly specify in their documentation any jaroslav@557: * restrictions on what elements may be added.

jaroslav@557: * jaroslav@557: * If a collection refuses to add a particular element for any reason jaroslav@557: * other than that it already contains the element, it must throw jaroslav@557: * an exception (rather than returning false). This preserves jaroslav@557: * the invariant that a collection always contains the specified element jaroslav@557: * after this call returns. jaroslav@557: * jaroslav@557: * @param e element whose presence in this collection is to be ensured jaroslav@557: * @return true if this collection changed as a result of the jaroslav@557: * call jaroslav@557: * @throws UnsupportedOperationException if the add operation jaroslav@557: * is not supported by this collection jaroslav@557: * @throws ClassCastException if the class of the specified element jaroslav@557: * prevents it from being added to this collection jaroslav@557: * @throws NullPointerException if the specified element is null and this jaroslav@557: * collection does not permit null elements jaroslav@557: * @throws IllegalArgumentException if some property of the element jaroslav@557: * prevents it from being added to this collection jaroslav@557: * @throws IllegalStateException if the element cannot be added at this jaroslav@557: * time due to insertion restrictions jaroslav@557: */ jaroslav@557: boolean add(E e); jaroslav@557: jaroslav@557: /** jaroslav@557: * Removes a single instance of the specified element from this jaroslav@557: * collection, if it is present (optional operation). More formally, jaroslav@557: * removes an element e such that jaroslav@557: * (o==null ? e==null : o.equals(e)), if jaroslav@557: * this collection contains one or more such elements. Returns jaroslav@557: * true if this collection contained the specified element (or jaroslav@557: * equivalently, if this collection changed as a result of the call). jaroslav@557: * jaroslav@557: * @param o element to be removed from this collection, if present jaroslav@557: * @return true if an element was removed as a result of this call jaroslav@557: * @throws ClassCastException if the type of the specified element jaroslav@557: * is incompatible with this collection jaroslav@557: * (optional) jaroslav@557: * @throws NullPointerException if the specified element is null and this jaroslav@557: * collection does not permit null elements jaroslav@557: * (optional) jaroslav@557: * @throws UnsupportedOperationException if the remove operation jaroslav@557: * is not supported by this collection jaroslav@557: */ jaroslav@557: boolean remove(Object o); jaroslav@557: jaroslav@557: jaroslav@557: // Bulk Operations jaroslav@557: jaroslav@557: /** jaroslav@557: * Returns true if this collection contains all of the elements jaroslav@557: * in the specified collection. jaroslav@557: * jaroslav@557: * @param c collection to be checked for containment in this collection jaroslav@557: * @return true if this collection contains all of the elements jaroslav@557: * in the specified collection jaroslav@557: * @throws ClassCastException if the types of one or more elements jaroslav@557: * in the specified collection are incompatible with this jaroslav@557: * collection jaroslav@557: * (optional) jaroslav@557: * @throws NullPointerException if the specified collection contains one jaroslav@557: * or more null elements and this collection does not permit null jaroslav@557: * elements jaroslav@557: * (optional), jaroslav@557: * or if the specified collection is null. jaroslav@557: * @see #contains(Object) jaroslav@557: */ jaroslav@557: boolean containsAll(Collection c); jaroslav@557: jaroslav@557: /** jaroslav@557: * Adds all of the elements in the specified collection to this collection jaroslav@557: * (optional operation). The behavior of this operation is undefined if jaroslav@557: * the specified collection is modified while the operation is in progress. jaroslav@557: * (This implies that the behavior of this call is undefined if the jaroslav@557: * specified collection is this collection, and this collection is jaroslav@557: * nonempty.) jaroslav@557: * jaroslav@557: * @param c collection containing elements to be added to this collection jaroslav@557: * @return true if this collection changed as a result of the call jaroslav@557: * @throws UnsupportedOperationException if the addAll operation jaroslav@557: * is not supported by this collection jaroslav@557: * @throws ClassCastException if the class of an element of the specified jaroslav@557: * collection prevents it from being added to this collection jaroslav@557: * @throws NullPointerException if the specified collection contains a jaroslav@557: * null element and this collection does not permit null elements, jaroslav@557: * or if the specified collection is null jaroslav@557: * @throws IllegalArgumentException if some property of an element of the jaroslav@557: * specified collection prevents it from being added to this jaroslav@557: * collection jaroslav@557: * @throws IllegalStateException if not all the elements can be added at jaroslav@557: * this time due to insertion restrictions jaroslav@557: * @see #add(Object) jaroslav@557: */ jaroslav@557: boolean addAll(Collection c); jaroslav@557: jaroslav@557: /** jaroslav@557: * Removes all of this collection's elements that are also contained in the jaroslav@557: * specified collection (optional operation). After this call returns, jaroslav@557: * this collection will contain no elements in common with the specified jaroslav@557: * collection. jaroslav@557: * jaroslav@557: * @param c collection containing elements to be removed from this collection jaroslav@557: * @return true if this collection changed as a result of the jaroslav@557: * call jaroslav@557: * @throws UnsupportedOperationException if the removeAll method jaroslav@557: * is not supported by this collection jaroslav@557: * @throws ClassCastException if the types of one or more elements jaroslav@557: * in this collection are incompatible with the specified jaroslav@557: * collection jaroslav@557: * (optional) jaroslav@557: * @throws NullPointerException if this collection contains one or more jaroslav@557: * null elements and the specified collection does not support jaroslav@557: * null elements jaroslav@557: * (optional), jaroslav@557: * or if the specified collection is null jaroslav@557: * @see #remove(Object) jaroslav@557: * @see #contains(Object) jaroslav@557: */ jaroslav@557: boolean removeAll(Collection c); jaroslav@557: jaroslav@557: /** jaroslav@557: * Retains only the elements in this collection that are contained in the jaroslav@557: * specified collection (optional operation). In other words, removes from jaroslav@557: * this collection all of its elements that are not contained in the jaroslav@557: * specified collection. jaroslav@557: * jaroslav@557: * @param c collection containing elements to be retained in this collection jaroslav@557: * @return true if this collection changed as a result of the call jaroslav@557: * @throws UnsupportedOperationException if the retainAll operation jaroslav@557: * is not supported by this collection jaroslav@557: * @throws ClassCastException if the types of one or more elements jaroslav@557: * in this collection are incompatible with the specified jaroslav@557: * collection jaroslav@557: * (optional) jaroslav@557: * @throws NullPointerException if this collection contains one or more jaroslav@557: * null elements and the specified collection does not permit null jaroslav@557: * elements jaroslav@557: * (optional), jaroslav@557: * or if the specified collection is null jaroslav@557: * @see #remove(Object) jaroslav@557: * @see #contains(Object) jaroslav@557: */ jaroslav@557: boolean retainAll(Collection c); jaroslav@557: jaroslav@557: /** jaroslav@557: * Removes all of the elements from this collection (optional operation). jaroslav@557: * The collection will be empty after this method returns. jaroslav@557: * jaroslav@557: * @throws UnsupportedOperationException if the clear operation jaroslav@557: * is not supported by this collection jaroslav@557: */ jaroslav@557: void clear(); jaroslav@557: jaroslav@557: jaroslav@557: // Comparison and hashing jaroslav@557: jaroslav@557: /** jaroslav@557: * Compares the specified object with this collection for equality.

jaroslav@557: * jaroslav@557: * While the Collection interface adds no stipulations to the jaroslav@557: * general contract for the Object.equals, programmers who jaroslav@557: * implement the Collection interface "directly" (in other words, jaroslav@557: * create a class that is a Collection but is not a Set jaroslav@557: * or a List) must exercise care if they choose to override the jaroslav@557: * Object.equals. It is not necessary to do so, and the simplest jaroslav@557: * course of action is to rely on Object's implementation, but jaroslav@557: * the implementor may wish to implement a "value comparison" in place of jaroslav@557: * the default "reference comparison." (The List and jaroslav@557: * Set interfaces mandate such value comparisons.)

jaroslav@557: * jaroslav@557: * The general contract for the Object.equals method states that jaroslav@557: * equals must be symmetric (in other words, a.equals(b) if and jaroslav@557: * only if b.equals(a)). The contracts for List.equals jaroslav@557: * and Set.equals state that lists are only equal to other lists, jaroslav@557: * and sets to other sets. Thus, a custom equals method for a jaroslav@557: * collection class that implements neither the List nor jaroslav@557: * Set interface must return false when this collection jaroslav@557: * is compared to any list or set. (By the same logic, it is not possible jaroslav@557: * to write a class that correctly implements both the Set and jaroslav@557: * List interfaces.) jaroslav@557: * jaroslav@557: * @param o object to be compared for equality with this collection jaroslav@557: * @return true if the specified object is equal to this jaroslav@557: * collection jaroslav@557: * jaroslav@557: * @see Object#equals(Object) jaroslav@557: * @see Set#equals(Object) jaroslav@557: * @see List#equals(Object) jaroslav@557: */ jaroslav@557: boolean equals(Object o); jaroslav@557: jaroslav@557: /** jaroslav@557: * Returns the hash code value for this collection. While the jaroslav@557: * Collection interface adds no stipulations to the general jaroslav@557: * contract for the Object.hashCode method, programmers should jaroslav@557: * take note that any class that overrides the Object.equals jaroslav@557: * method must also override the Object.hashCode method in order jaroslav@557: * to satisfy the general contract for the Object.hashCode method. jaroslav@557: * In particular, c1.equals(c2) implies that jaroslav@557: * c1.hashCode()==c2.hashCode(). jaroslav@557: * jaroslav@557: * @return the hash code value for this collection jaroslav@557: * jaroslav@557: * @see Object#hashCode() jaroslav@557: * @see Object#equals(Object) jaroslav@557: */ jaroslav@557: int hashCode(); jaroslav@557: }