--- jsr166/src/jsr166x/Deque.java 2004/09/07 10:37:29 1.2 +++ jsr166/src/jsr166x/Deque.java 2004/12/05 21:15:31 1.3 @@ -1,121 +1,222 @@ /* - * Written by Doug Lea with assistance from members of JCP JSR-166 - * Expert Group and released to the public domain, as explained at - * http://creativecommons.org/licenses/publicdomain + * 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 */ -package jsr166x; -import java.util.*; +package jsr166x; // XXX This belongs in java.util!!! XXX +import java.util.*; // XXX This import goes away XXX /** - * A linear collection in which elements may be inserted and removed - * from both the beginning and end. A Deque (short for - * "double ended queue") provides uniformly named methods to - * get, peek, poll, remove, - * offer, and add the first and - * last element of the collection (for example, methods - * addFirst, pollLast). Unlike interface {@link - * List} the Deque interface does not define support for indexed - * operations or sublists. - * - *
A view of a subset of Deque operations can be obtained using - * method {@link #asFifoQueue} to support only Last-In-First-Out (LIFO) - * stack behavior, as well as method {@link #asFifoQueue} to support only - * First-in-First-Out (FIFO) queue behavior. More commonly, a Deque - * is used when various mixtures of LIFO and FIFO operations are - * required. - * - *
Deques additionally provide a few methods to remove elements - * embedded within a deque, proceding from either direction using - * removeFirstOccurrence and removeLastOccurrence. - * They also support {@link Collection} operations including - * contains, iterator, and so on. - * - *
The {@link #offerFirst} and {@link #offerLast} methods insert an - * element if possible, otherwise returning false. They - * differ from {@link java.util.Collection#add Collection.add}, as - * well as {@link #addFirst} and {@link #addLast} methods, which can - * fail to add an element only by throwing an unchecked exception. - * The offer methods are designed for use when failure is a - * normal, rather than exceptional occurrence, for example, in - * fixed-capacity (or "bounded") deques. - * - *
Deque implementations generally do not allow insertion - * of null elements. Even in implementations that permit it, - * null should not be inserted into a Deque, as - * null is also used as a special return value by the poll - * methods to indicate that the deque contains no elements. + * 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 + * 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. + * + *
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 + * null or 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 operations cannot fail. + * + *
The twelve methods described above are are summarized in the + * follwoing table:
+ * + *
+ * | First Element (Head) | + *Last Element (Tail) | + *||
+ * | Throws exception | + *Returns special value | + *Throws exception | + *Returns special value | + *
Insert | + *{@link #addFirst addFirst(e)} | + *{@link #offerFirst offerFirst(e)} | + *{@link #addLast addLast(e)} | + *{@link #offerLast offerLast(e)} | + *
Remove | + *{@link #removeFirst removeFirst()} | + *{@link #pollFirst pollFirst()} | + *{@link #removeLast removeLast()} | + *{@link #pollLast pollLast()} | + *
Examine | + *{@link #firstElement firstElement()} | + *{@link #peekFirst peekFirst()} | + *{@link #lastElement lastElement()} | + *{@link #peekLast peekLast()} | + *
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 to 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:
+ * + *
Queue Method | + *Equivalent Deque Method | + *
{@link java.util.Queue#offer offer(e)} | + *{@link #offerLast offerLast(e)} | + *
{@link java.util.Queue#add add(e)} | + *{@link #addLast addLast(e)} | + *
{@link java.util.Queue#poll poll()} | + *{@link #pollFirst pollFirst()} | + *
{@link java.util.Queue#remove remove()} | + *{@link #removeFirst removeFirst()} | + *
{@link java.util.Queue#peek peek()} | + *{@link #peek peekFirst()} | + *
{@link java.util.Queue#element element()} | + *{@link #firstElement firstElement()} | + *
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 dequeue 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:
+ * + *
Stack Method | + *Equivalent Deque Method | + *
{@link #push push(e)} | + *{@link #addFirst addFirst(e)} | + *
{@link #pop pop()} | + *{@link #removeFirst removeFirst()} | + *
{@link #peek peek()} | + *{@link #peekFirst peekFirst()} | + *
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. + * + *
This inteface provides two methods to to remove interior elements, + * {@link #removeFirstOccurrence removeFirstOccurrence} and {@link + * #removeLastOccurrence removeLastOccurrence}. Unlike the {@link List} + * interface, this interface does not provide support for indexed access to + * elements. + * + *
While 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 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 to indicated that the deque is + * empty. * *
Deque implementations generally do not define - * element-based versions of methods equals and - * hashCode but instead inherit the identity based versions - * from class Object. + * element-based versions of the equals and hashCode + * methods, but instead inherit the identity-based versions from class + * Object. * *
This interface is a member of the Java Collections
* Framework.
*
* @author Doug Lea
+ * @author Josh Bloch
+ * @since 1.6
* @param This method is equivalent to {@link #offerLast}.
+ *
+ * @param e the element to insert
+ * @return true if it was possible to insert the element,
+ * else false
+ * @throws NullPointerException if e is null and this
+ * deque does not permit null elements
*/
- public Queue This method is equivalent to {@link #addLast}.
+ *
+ * @param e the element to insert
+ * @return true (as per the spec for {@link Collection#add})
+ * @throws IllegalStateException if it was not possible to insert
+ * the element due to capacity restrictions
+ * @throws NullPointerException if e is null and this
+ * deque does not permit null elements
+ */
+ boolean add(E e);
+
+ /**
+ * Retrieves and removes the head of the queue represented by
+ * this deque, or null if this deque is empty. In other words,
+ * retrieves and removes the first element of this deque, or null
+ * if this deque is empty.
+ *
+ * This method is equivalent to {@link #pollFirst()}.
+ *
+ * @return the first element of this deque, or null if
+ * this deque is empty
+ */
+ E poll();
+
+ /**
+ * Retrieves and removes the head of the queue represented by this deque.
+ * This method differs from the poll method only in that it
+ * throws an exception if this deque is empty.
+ *
+ * This method is equivalent to {@link #removeFirst()}.
+ *
+ * @return the head of the queue represented by this deque
+ * @throws NoSuchElementException if this deque is empty
*/
- public Queue This method is equivalent to {@link #peekFirst()}
+ *
+ * @return the head of the queue represented by this deque, or
+ * null if this deque is empty
+ */
+ E peek();
+
+ /**
+ * Retrieves, but does not remove, the head of the queue represented by
+ * this deque. This method differs from the peek method only in
+ * that it throws an exception if this deque is empty.
+ *
+ * This method is equivalent to {@link #firstElement()}
+ *
+ * @return the head of the queue represented by this deque
+ * @throws NoSuchElementException if this deque is empty
+ */
+ E element();
+
+
+ // *** Stack methods ***
+
+ /**
+ * Pushes an element onto the stack represented by this deque. In other
+ * words, inserts the element to the front this deque unless it would
+ * violate capacity restrictions.
+ *
+ * This method is equivalent to {@link #addFirst}.
+ *
+ * @throws IllegalStateException if it was not possible to insert
+ * the element due to capacity restrictions
+ * @throws NullPointerException if e is null and this
+ * deque does not permit null elements
+ */
+ void push(E e);
+
+ /**
+ * Pops an element from the stack represented by this deque. In other
+ * words, removes and returns the the first element of this deque.
+ *
+ * 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 Method ***
+
+ /**
+ * Returns an iterator over the elements in this deque. The elements
+ * will be ordered from first (head) to last (tail).
+ *
+ * @return an Iterator over the elements in this deque
+ */
+ Iterator