--- jsr166/src/main/java/util/Deque.java 2005/06/18 01:56:01 1.14 +++ jsr166/src/main/java/util/Deque.java 2013/05/02 06:38:33 1.25 @@ -1,16 +1,15 @@ /* * 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/licenses/publicdomain + * at http://creativecommons.org/publicdomain/zero/1.0/ */ package java.util; -import java.util.*; // for javadoc /** * A linear collection that supports element insertion and removal at * both ends. The name deque is short for "double ended queue" - * and is usually pronounced "deck". Most Deque + * 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. @@ -19,10 +18,10 @@ import java.util.*; // for javadoc * 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 null or false, depending on + * 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 - * Deque implementations; in most implementations, insert + * {@code Deque} implementations; in most implementations, insert * operations cannot fail. * *

The twelve methods described above are summarized in the @@ -30,6 +29,7 @@ import java.util.*; // for javadoc * *

* + * * * * @@ -68,14 +68,15 @@ import java.util.*; // for javadoc *

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 Queue interface are precisely equivalent to - * Deque methods as indicated in the following table: + * inherited from the {@code Queue} interface are precisely equivalent to + * {@code Deque} methods as indicated in the following table: * *

*

Summary of Deque methods
First Element (Head)
+ * * - * - * + * + * * * * @@ -107,13 +108,14 @@ import java.util.*; // for javadoc * 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 - * Deque methods as indicated in the table below: + * {@code Deque} methods as indicated in the table below: * *

*

Comparison of Queue and Deque methods
Queue Method Equivalent Deque Method {@code Queue} Method Equivalent {@code Deque} Method
{@link java.util.Queue#add add(e)}
+ * * * - * + * * * * @@ -140,21 +142,21 @@ import java.util.*; // for javadoc *

Unlike the {@link List} interface, this interface does not * provide support for indexed access to elements. * - *

While Deque implementations are not strictly required + *

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 Deque implementations + * encouraged to do so. Users of any {@code Deque} implementations * that do allow null elements are strongly encouraged not to * take advantage of the ability to insert nulls. This is so because - * null is used as a special return value by various methods + * {@code null} is used as a special return value by various methods * to indicated that the deque is empty. * - *

Deque implementations generally do not define - * element-based versions of the equals and hashCode + *

{@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 - * Object. + * {@code Object}. * *

This interface is a member of the Java Collections + * href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections * Framework. * * @author Doug Lea @@ -162,13 +164,13 @@ import java.util.*; // for javadoc * @since 1.6 * @param the type of elements held in this collection */ - public interface Deque extends Queue { /** * Inserts the specified element at the front of this deque if it is - * possible to do so immediately without violating capacity restrictions. - * When using a capacity-restricted deque, it is generally preferable to - * use method {@link #offerFirst}. + * 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 @@ -184,9 +186,10 @@ public interface Deque extends Queue< /** * Inserts the specified element at the end of this deque if it is - * possible to do so immediately without violating capacity restrictions. - * When using a capacity-restricted deque, it is generally preferable to - * use method {@link #offerLast}. + * 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}. * *

This method is equivalent to {@link #add}. * @@ -209,8 +212,8 @@ public interface Deque extends Queue< * which can fail to insert an element only by throwing an exception. * * @param e the element to add - * @return true if the element was added to this deque, else - * false + * @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 @@ -227,8 +230,8 @@ public interface Deque extends Queue< * which can fail to insert an element only by throwing an exception. * * @param e the element to add - * @return true if the element was added to this deque, else - * false + * @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 @@ -240,8 +243,8 @@ public interface Deque extends Queue< /** * Retrieves and removes the first element of this deque. This method - * differs from {@link #pollFirst} only in that it throws an exception - * if this deque is empty. + * 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 @@ -250,8 +253,8 @@ public interface Deque extends Queue< /** * Retrieves and removes the last element of this deque. This method - * differs from {@link #pollLast} only in that it throws an exception if - * this deque is empty. + * 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 @@ -260,24 +263,25 @@ public interface Deque extends Queue< /** * Retrieves and removes the first element of this deque, - * or returns null if this deque is empty. + * or returns {@code null} if this deque is empty. * - * @return the head of this deque, or 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 null if this deque is empty. + * or returns {@code null} if this deque is empty. * - * @return the tail of this deque, or 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} only in that it throws an - * exception if this deque is empty. + * + * 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 @@ -286,8 +290,8 @@ public interface Deque extends Queue< /** * Retrieves, but does not remove, the last element of this deque. - * This method differs from {@link #peekLast} only in that it throws an - * exception if this deque is empty. + * 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 @@ -296,31 +300,31 @@ public interface Deque extends Queue< /** * Retrieves, but does not remove, the first element of this deque, - * or returns null if this deque is empty. + * or returns {@code null} if this deque is empty. * - * @return the head of this deque, or 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 null if this deque is empty. + * or returns {@code null} if this deque is empty. * - * @return the tail of this deque, or 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 e such that + * More formally, removes the first element {@code e} such that * (o==null ? e==null : o.equals(e)) * (if such an element exists). - * Returns true if this deque contained the specified element + * 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 true if an element was removed as a result of this call + * @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 (optional) * @throws NullPointerException if the specified element is null and this @@ -331,14 +335,14 @@ public interface Deque extends Queue< /** * 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 e such that + * More formally, removes the last element {@code e} such that * (o==null ? e==null : o.equals(e)) * (if such an element exists). - * Returns true if this deque contained the specified element + * 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 true if an element was removed as a result of this call + * @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 (optional) * @throws NullPointerException if the specified element is null and this @@ -352,15 +356,15 @@ public interface Deque extends Queue< * 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 - * true upon success and throwing an - * IllegalStateException if no space is currently available. + * {@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}. * *

This method is equivalent to {@link #addLast}. * * @param e the element to add - * @return true (as per the spec for {@link Collection#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 @@ -376,7 +380,7 @@ public interface Deque extends Queue< * 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 - * true upon success and false if no space is currently + * {@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. @@ -384,8 +388,8 @@ public interface Deque extends Queue< *

This method is equivalent to {@link #offerLast}. * * @param e the element to add - * @return true if the element was added to this deque, else - * false + * @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 @@ -398,7 +402,7 @@ public interface Deque extends Queue< /** * 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} only in that it throws an + * This method differs from {@link #poll poll} only in that it throws an * exception if this deque is empty. * *

This method is equivalent to {@link #removeFirst()}. @@ -411,11 +415,11 @@ public interface Deque extends Queue< /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque), or returns - * null if this deque is empty. + * {@code null} if this deque is empty. * *

This method is equivalent to {@link #pollFirst()}. * - * @return the first element of this deque, or null if + * @return the first element of this deque, or {@code null} if * this deque is empty */ E poll(); @@ -423,7 +427,7 @@ public interface Deque extends Queue< /** * 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} only in that it throws an + * This method differs from {@link #peek peek} only in that it throws an * exception if this deque is empty. * *

This method is equivalent to {@link #getFirst()}. @@ -436,12 +440,12 @@ public interface Deque extends Queue< /** * 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 null if this deque is empty. + * returns {@code null} if this deque is empty. * *

This method is equivalent to {@link #peekFirst()}. * * @return the head of the queue represented by this deque, or - * null if this deque is empty + * {@code null} if this deque is empty */ E peek(); @@ -451,9 +455,8 @@ public interface Deque extends Queue< /** * 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, returning - * true upon success and throwing an - * IllegalStateException if no space is currently available. + * immediately without violating capacity restrictions, throwing an + * {@code IllegalStateException} if no space is currently available. * *

This method is equivalent to {@link #addFirst}. * @@ -487,16 +490,16 @@ public interface Deque extends Queue< /** * 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 e such that + * More formally, removes the first element {@code e} such that * (o==null ? e==null : o.equals(e)) * (if such an element exists). - * Returns true if this deque contained the specified element + * Returns {@code true} if this deque contained the specified element * (or equivalently, if this deque changed as a result of the call). * - *

This method is equivalent to {@link #removeFirstOccurrence}. + *

This method is equivalent to {@link #removeFirstOccurrence(Object)}. * * @param o element to be removed from this deque, if present - * @return true if an element was removed as a result of this call + * @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 (optional) * @throws NullPointerException if the specified element is null and this @@ -505,13 +508,13 @@ public interface Deque extends Queue< boolean remove(Object o); /** - * Returns true if this deque contains the specified element. - * More formally, returns true if and only if this deque contains - * at least one element e such that + * 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 * (o==null ? e==null : o.equals(e)). * * @param o element whose presence in this deque is to be tested - * @return true if this deque contains the specified element + * @return {@code true} if this deque contains the specified element * @throws ClassCastException if the type of the specified element * is incompatible with this deque (optional) * @throws NullPointerException if the specified element is null and this @@ -533,4 +536,15 @@ public interface Deque extends Queue< * @return an iterator over the elements in this deque in proper sequence */ Iterator 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 descendingIterator(); + }

Comparison of Stack and Deque methods
Stack Method Equivalent Deque Method Equivalent {@code Deque} Method
{@link #push push(e)}