| /* |
| * 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. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea and Josh Bloch with assistance from members of |
| * JCP JSR-166 Expert Group and released to the public domain, as explained |
| * at http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util; |
| |
| /** |
| * A linear collection that supports element insertion and removal at |
| * both ends. The name <i>deque</i> is short for "double ended queue" |
| * and is usually pronounced "deck". Most {@code Deque} |
| * implementations place no fixed limits on the number of elements |
| * they may contain, but this interface supports capacity-restricted |
| * deques as well as those with no fixed size limit. |
| * |
| * <p>This interface defines methods to access the elements at both |
| * ends of the deque. Methods are provided to insert, remove, and |
| * examine the element. Each of these methods exists in two forms: |
| * one throws an exception if the operation fails, the other returns a |
| * special value (either {@code null} or {@code false}, depending on |
| * the operation). The latter form of the insert operation is |
| * designed specifically for use with capacity-restricted |
| * {@code Deque} implementations; in most implementations, insert |
| * operations cannot fail. |
| * |
| * <p>The twelve methods described above are summarized in the |
| * following table: |
| * |
| * <table BORDER CELLPADDING=3 CELLSPACING=1> |
| * <caption>Summary of Deque methods</caption> |
| * <tr> |
| * <td></td> |
| * <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td> |
| * <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td> |
| * </tr> |
| * <tr> |
| * <td></td> |
| * <td ALIGN=CENTER><em>Throws exception</em></td> |
| * <td ALIGN=CENTER><em>Special value</em></td> |
| * <td ALIGN=CENTER><em>Throws exception</em></td> |
| * <td ALIGN=CENTER><em>Special value</em></td> |
| * </tr> |
| * <tr> |
| * <td><b>Insert</b></td> |
| * <td>{@link Deque#addFirst addFirst(e)}</td> |
| * <td>{@link Deque#offerFirst offerFirst(e)}</td> |
| * <td>{@link Deque#addLast addLast(e)}</td> |
| * <td>{@link Deque#offerLast offerLast(e)}</td> |
| * </tr> |
| * <tr> |
| * <td><b>Remove</b></td> |
| * <td>{@link Deque#removeFirst removeFirst()}</td> |
| * <td>{@link Deque#pollFirst pollFirst()}</td> |
| * <td>{@link Deque#removeLast removeLast()}</td> |
| * <td>{@link Deque#pollLast pollLast()}</td> |
| * </tr> |
| * <tr> |
| * <td><b>Examine</b></td> |
| * <td>{@link Deque#getFirst getFirst()}</td> |
| * <td>{@link Deque#peekFirst peekFirst()}</td> |
| * <td>{@link Deque#getLast getLast()}</td> |
| * <td>{@link Deque#peekLast peekLast()}</td> |
| * </tr> |
| * </table> |
| * |
| * <p>This interface extends the {@link Queue} interface. When a deque is |
| * used as a queue, FIFO (First-In-First-Out) behavior results. Elements are |
| * added at the end of the deque and removed from the beginning. The methods |
| * inherited from the {@code Queue} interface are precisely equivalent to |
| * {@code Deque} methods as indicated in the following table: |
| * |
| * <table BORDER CELLPADDING=3 CELLSPACING=1> |
| * <caption>Comparison of Queue and Deque methods</caption> |
| * <tr> |
| * <td ALIGN=CENTER> <b>{@code Queue} Method</b></td> |
| * <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td> |
| * </tr> |
| * <tr> |
| * <td>{@link java.util.Queue#add add(e)}</td> |
| * <td>{@link #addLast addLast(e)}</td> |
| * </tr> |
| * <tr> |
| * <td>{@link java.util.Queue#offer offer(e)}</td> |
| * <td>{@link #offerLast offerLast(e)}</td> |
| * </tr> |
| * <tr> |
| * <td>{@link java.util.Queue#remove remove()}</td> |
| * <td>{@link #removeFirst removeFirst()}</td> |
| * </tr> |
| * <tr> |
| * <td>{@link java.util.Queue#poll poll()}</td> |
| * <td>{@link #pollFirst pollFirst()}</td> |
| * </tr> |
| * <tr> |
| * <td>{@link java.util.Queue#element element()}</td> |
| * <td>{@link #getFirst getFirst()}</td> |
| * </tr> |
| * <tr> |
| * <td>{@link java.util.Queue#peek peek()}</td> |
| * <td>{@link #peek peekFirst()}</td> |
| * </tr> |
| * </table> |
| * |
| * <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This |
| * interface should be used in preference to the legacy {@link Stack} class. |
| * When a deque is used as a stack, elements are pushed and popped from the |
| * beginning of the deque. Stack methods are precisely equivalent to |
| * {@code Deque} methods as indicated in the table below: |
| * |
| * <table BORDER CELLPADDING=3 CELLSPACING=1> |
| * <caption>Comparison of Stack and Deque methods</caption> |
| * <tr> |
| * <td ALIGN=CENTER> <b>Stack Method</b></td> |
| * <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td> |
| * </tr> |
| * <tr> |
| * <td>{@link #push push(e)}</td> |
| * <td>{@link #addFirst addFirst(e)}</td> |
| * </tr> |
| * <tr> |
| * <td>{@link #pop pop()}</td> |
| * <td>{@link #removeFirst removeFirst()}</td> |
| * </tr> |
| * <tr> |
| * <td>{@link #peek peek()}</td> |
| * <td>{@link #peekFirst peekFirst()}</td> |
| * </tr> |
| * </table> |
| * |
| * <p>Note that the {@link #peek peek} method works equally well when |
| * a deque is used as a queue or a stack; in either case, elements are |
| * drawn from the beginning of the deque. |
| * |
| * <p>This interface provides two methods to remove interior |
| * elements, {@link #removeFirstOccurrence removeFirstOccurrence} and |
| * {@link #removeLastOccurrence removeLastOccurrence}. |
| * |
| * <p>Unlike the {@link List} interface, this interface does not |
| * provide support for indexed access to elements. |
| * |
| * <p>While {@code Deque} implementations are not strictly required |
| * to prohibit the insertion of null elements, they are strongly |
| * encouraged to do so. Users of any {@code Deque} implementations |
| * that do allow null elements are strongly encouraged <i>not</i> to |
| * take advantage of the ability to insert nulls. This is so because |
| * {@code null} is used as a special return value by various methods |
| * to indicated that the deque is empty. |
| * |
| * <p>{@code Deque} implementations generally do not define |
| * element-based versions of the {@code equals} and {@code hashCode} |
| * methods, but instead inherit the identity-based versions from class |
| * {@code Object}. |
| * |
| * <p>This interface is a member of the <a |
| * href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections |
| * Framework</a>. |
| * |
| * @author Doug Lea |
| * @author Josh Bloch |
| * @since 1.6 |
| * @param <E> the type of elements held in this collection |
| */ |
| public interface Deque<E> extends Queue<E> { |
| /** |
| * Inserts the specified element at the front of this deque if it is |
| * possible to do so immediately without violating capacity restrictions, |
| * throwing an {@code IllegalStateException} if no space is currently |
| * available. When using a capacity-restricted deque, it is generally |
| * preferable to use method {@link #offerFirst}. |
| * |
| * @param e the element to add |
| * @throws IllegalStateException if the element cannot be added at this |
| * time due to capacity restrictions |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this deque |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this deque |
| */ |
| void addFirst(E e); |
| |
| /** |
| * Inserts the specified element at the end of this deque if it is |
| * possible to do so immediately without violating capacity restrictions, |
| * throwing an {@code IllegalStateException} if no space is currently |
| * available. When using a capacity-restricted deque, it is generally |
| * preferable to use method {@link #offerLast}. |
| * |
| * <p>This method is equivalent to {@link #add}. |
| * |
| * @param e the element to add |
| * @throws IllegalStateException if the element cannot be added at this |
| * time due to capacity restrictions |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this deque |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this deque |
| */ |
| void addLast(E e); |
| |
| /** |
| * Inserts the specified element at the front of this deque unless it would |
| * violate capacity restrictions. When using a capacity-restricted deque, |
| * this method is generally preferable to the {@link #addFirst} method, |
| * which can fail to insert an element only by throwing an exception. |
| * |
| * @param e the element to add |
| * @return {@code true} if the element was added to this deque, else |
| * {@code false} |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this deque |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this deque |
| */ |
| boolean offerFirst(E e); |
| |
| /** |
| * Inserts the specified element at the end of this deque unless it would |
| * violate capacity restrictions. When using a capacity-restricted deque, |
| * this method is generally preferable to the {@link #addLast} method, |
| * which can fail to insert an element only by throwing an exception. |
| * |
| * @param e the element to add |
| * @return {@code true} if the element was added to this deque, else |
| * {@code false} |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this deque |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this deque |
| */ |
| boolean offerLast(E e); |
| |
| /** |
| * Retrieves and removes the first element of this deque. This method |
| * differs from {@link #pollFirst pollFirst} only in that it throws an |
| * exception if this deque is empty. |
| * |
| * @return the head of this deque |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| E removeFirst(); |
| |
| /** |
| * Retrieves and removes the last element of this deque. This method |
| * differs from {@link #pollLast pollLast} only in that it throws an |
| * exception if this deque is empty. |
| * |
| * @return the tail of this deque |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| E removeLast(); |
| |
| /** |
| * Retrieves and removes the first element of this deque, |
| * or returns {@code null} if this deque is empty. |
| * |
| * @return the head of this deque, or {@code null} if this deque is empty |
| */ |
| E pollFirst(); |
| |
| /** |
| * Retrieves and removes the last element of this deque, |
| * or returns {@code null} if this deque is empty. |
| * |
| * @return the tail of this deque, or {@code null} if this deque is empty |
| */ |
| E pollLast(); |
| |
| /** |
| * Retrieves, but does not remove, the first element of this deque. |
| * |
| * This method differs from {@link #peekFirst peekFirst} only in that it |
| * throws an exception if this deque is empty. |
| * |
| * @return the head of this deque |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| E getFirst(); |
| |
| /** |
| * Retrieves, but does not remove, the last element of this deque. |
| * This method differs from {@link #peekLast peekLast} only in that it |
| * throws an exception if this deque is empty. |
| * |
| * @return the tail of this deque |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| E getLast(); |
| |
| /** |
| * Retrieves, but does not remove, the first element of this deque, |
| * or returns {@code null} if this deque is empty. |
| * |
| * @return the head of this deque, or {@code null} if this deque is empty |
| */ |
| E peekFirst(); |
| |
| /** |
| * Retrieves, but does not remove, the last element of this deque, |
| * or returns {@code null} if this deque is empty. |
| * |
| * @return the tail of this deque, or {@code null} if this deque is empty |
| */ |
| E peekLast(); |
| |
| /** |
| * Removes the first occurrence of the specified element from this deque. |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the first element {@code e} such that |
| * <tt>(o==null ? e==null : o.equals(e))</tt> |
| * (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * @param o element to be removed from this deque, if present |
| * @return {@code true} if an element was removed as a result of this call |
| * @throws ClassCastException if the class of the specified element |
| * is incompatible with this deque |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| */ |
| boolean removeFirstOccurrence(Object o); |
| |
| /** |
| * Removes the last occurrence of the specified element from this deque. |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the last element {@code e} such that |
| * <tt>(o==null ? e==null : o.equals(e))</tt> |
| * (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * @param o element to be removed from this deque, if present |
| * @return {@code true} if an element was removed as a result of this call |
| * @throws ClassCastException if the class of the specified element |
| * is incompatible with this deque |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| */ |
| boolean removeLastOccurrence(Object o); |
| |
| // *** Queue methods *** |
| |
| /** |
| * Inserts the specified element into the queue represented by this deque |
| * (in other words, at the tail of this deque) if it is possible to do so |
| * immediately without violating capacity restrictions, returning |
| * {@code true} upon success and throwing an |
| * {@code IllegalStateException} if no space is currently available. |
| * When using a capacity-restricted deque, it is generally preferable to |
| * use {@link #offer(Object) offer}. |
| * |
| * <p>This method is equivalent to {@link #addLast}. |
| * |
| * @param e the element to add |
| * @return {@code true} (as specified by {@link Collection#add}) |
| * @throws IllegalStateException if the element cannot be added at this |
| * time due to capacity restrictions |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this deque |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this deque |
| */ |
| boolean add(E e); |
| |
| /** |
| * Inserts the specified element into the queue represented by this deque |
| * (in other words, at the tail of this deque) if it is possible to do so |
| * immediately without violating capacity restrictions, returning |
| * {@code true} upon success and {@code false} if no space is currently |
| * available. When using a capacity-restricted deque, this method is |
| * generally preferable to the {@link #add} method, which can fail to |
| * insert an element only by throwing an exception. |
| * |
| * <p>This method is equivalent to {@link #offerLast}. |
| * |
| * @param e the element to add |
| * @return {@code true} if the element was added to this deque, else |
| * {@code false} |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this deque |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this deque |
| */ |
| boolean offer(E e); |
| |
| /** |
| * Retrieves and removes the head of the queue represented by this deque |
| * (in other words, the first element of this deque). |
| * This method differs from {@link #poll poll} only in that it throws an |
| * exception if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #removeFirst()}. |
| * |
| * @return the head of the queue represented by this deque |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| E remove(); |
| |
| /** |
| * Retrieves and removes the head of the queue represented by this deque |
| * (in other words, the first element of this deque), or returns |
| * {@code null} if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #pollFirst()}. |
| * |
| * @return the first element of this deque, or {@code null} if |
| * this deque is empty |
| */ |
| E poll(); |
| |
| /** |
| * Retrieves, but does not remove, the head of the queue represented by |
| * this deque (in other words, the first element of this deque). |
| * This method differs from {@link #peek peek} only in that it throws an |
| * exception if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #getFirst()}. |
| * |
| * @return the head of the queue represented by this deque |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| E element(); |
| |
| /** |
| * Retrieves, but does not remove, the head of the queue represented by |
| * this deque (in other words, the first element of this deque), or |
| * returns {@code null} if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #peekFirst()}. |
| * |
| * @return the head of the queue represented by this deque, or |
| * {@code null} if this deque is empty |
| */ |
| E peek(); |
| |
| |
| // *** Stack methods *** |
| |
| /** |
| * Pushes an element onto the stack represented by this deque (in other |
| * words, at the head of this deque) if it is possible to do so |
| * immediately without violating capacity restrictions, throwing an |
| * {@code IllegalStateException} if no space is currently available. |
| * |
| * <p>This method is equivalent to {@link #addFirst}. |
| * |
| * @param e the element to push |
| * @throws IllegalStateException if the element cannot be added at this |
| * time due to capacity restrictions |
| * @throws ClassCastException if the class of the specified element |
| * prevents it from being added to this deque |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * @throws IllegalArgumentException if some property of the specified |
| * element prevents it from being added to this deque |
| */ |
| void push(E e); |
| |
| /** |
| * Pops an element from the stack represented by this deque. In other |
| * words, removes and returns the first element of this deque. |
| * |
| * <p>This method is equivalent to {@link #removeFirst()}. |
| * |
| * @return the element at the front of this deque (which is the top |
| * of the stack represented by this deque) |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| E pop(); |
| |
| |
| // *** Collection methods *** |
| |
| /** |
| * Removes the first occurrence of the specified element from this deque. |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the first element {@code e} such that |
| * <tt>(o==null ? e==null : o.equals(e))</tt> |
| * (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. |
| * |
| * @param o element to be removed from this deque, if present |
| * @return {@code true} if an element was removed as a result of this call |
| * @throws ClassCastException if the class of the specified element |
| * is incompatible with this deque |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| */ |
| boolean remove(Object o); |
| |
| /** |
| * Returns {@code true} if this deque contains the specified element. |
| * More formally, returns {@code true} if and only if this deque contains |
| * at least one element {@code e} such that |
| * <tt>(o==null ? e==null : o.equals(e))</tt>. |
| * |
| * @param o element whose presence in this deque is to be tested |
| * @return {@code true} if this deque contains the specified element |
| * @throws ClassCastException if the type of the specified element |
| * is incompatible with this deque |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| * @throws NullPointerException if the specified element is null and this |
| * deque does not permit null elements |
| * (<a href="Collection.html#optional-restrictions">optional</a>) |
| */ |
| boolean contains(Object o); |
| |
| /** |
| * Returns the number of elements in this deque. |
| * |
| * @return the number of elements in this deque |
| */ |
| public int size(); |
| |
| /** |
| * Returns an iterator over the elements in this deque in proper sequence. |
| * The elements will be returned in order from first (head) to last (tail). |
| * |
| * @return an iterator over the elements in this deque in proper sequence |
| */ |
| Iterator<E> iterator(); |
| |
| /** |
| * Returns an iterator over the elements in this deque in reverse |
| * sequential order. The elements will be returned in order from |
| * last (tail) to first (head). |
| * |
| * @return an iterator over the elements in this deque in reverse |
| * sequence |
| */ |
| Iterator<E> descendingIterator(); |
| |
| } |
