The twelve methods described above are summarized in the - * following table:
+ * following table: * - *
| - * | First Element (Head) | - *Last Element (Tail) | + *First Element (Head) | + *Last Element (Tail) | *||||
| - * | Throws exception | - *Returns special value | - *Throws exception | - *Returns special value | + *Throws exception | + *Special value | + *Throws exception | + *Special value | *
| Insert | - *{@link #addFirst addFirst(e)} | - *{@link #offerFirst offerFirst(e)} | - *{@link #addLast addLast(e)} | - *{@link #offerLast offerLast(e)} | + *{@link #addFirst(Object) addFirst(e)} | + *{@link #offerFirst(Object) offerFirst(e)} | + *{@link #addLast(Object) addLast(e)} | + *{@link #offerLast(Object) offerLast(e)} | *
| Remove | - *{@link #removeFirst removeFirst()} | - *{@link #pollFirst pollFirst()} | - *{@link #removeLast removeLast()} | - *{@link #pollLast pollLast()} | + *{@link #removeFirst() removeFirst()} | + *{@link #pollFirst() pollFirst()} | + *{@link #removeLast() removeLast()} | + *{@link #pollLast() pollLast()} | *
| Examine | - *{@link #getFirst getFirst()} | - *{@link #peekFirst peekFirst()} | - *{@link #getLast getLast()} | - *{@link #peekLast peekLast()} | + *{@link #getFirst() getFirst()} | + *{@link #peekFirst() peekFirst()} | + *{@link #getLast() getLast()} | + *{@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 #getFirst getFirst()} | - *
| {@code Queue} Method | + *Equivalent {@code Deque} Method | + *
| {@link #add(Object) add(e)} | + *{@link #addLast(Object) addLast(e)} | + *
| {@link #offer(Object) offer(e)} | + *{@link #offerLast(Object) offerLast(e)} | + *
| {@link #remove() remove()} | + *{@link #removeFirst() removeFirst()} | + *
| {@link #poll() poll()} | + *{@link #pollFirst() pollFirst()} | + *
| {@link #element() element()} | + *{@link #getFirst() getFirst()} | + *
| {@link #peek() peek()} | + *{@link #peekFirst() peekFirst()} | + *
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 - * Deque methods as indicated in the table below:
+ * {@code Deque} methods as indicated in the table below: * - *
| Stack Method | - *Equivalent Deque Method | + *Stack Method | + *Equivalent {@code Deque} Method | *
| {@link #push push(e)} | - *{@link #addFirst addFirst(e)} | - *||
| {@link #pop pop()} | - *{@link #removeFirst removeFirst()} | - *||
| {@link #peek peek()} | - *{@link #peekFirst peekFirst()} | - *{@link #push(Object) push(e)} | + *{@link #addFirst(Object) 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 @@ -133,241 +134,274 @@ package java.util; * *
This interface provides two methods 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. + * {@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 + *
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 - * to indicated that the deque is empty. + * {@code null} is used as a special return value by various methods + * to indicate 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 - * Framework. + *
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 #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 method addFirst, which
- * can fail to insert an element only by throwing an exception.
+ * 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 insert
- * @return true if it was possible to insert the element,
- * else false
+ * @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
+ * 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 to the end of this deque unless it would
+ * 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 method addLast which
- * can fail to insert an element only by throwing an exception.
+ * 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 insert
- * @return true if it was possible to insert the element,
- * else false
+ * @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
+ * 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);
/**
- * Inserts the specified element at the front of this deque unless it
- * would violate capacity restrictions.
+ * 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.
*
- * @param e the element to insert
- * @throws IllegalStateException if it was not possible to insert
- * the element due to capacity restrictions
- * @throws NullPointerException if the specified element is null and this
- * deque does not permit null elements
+ * @return the head of this deque
+ * @throws NoSuchElementException if this deque is empty
*/
- void addFirst(E e);
+ E removeFirst();
/**
- * Inserts the specified element to the end of this deque unless it would
- * violate capacity restrictions.
+ * 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.
*
- * @param e the element to insert
- * @throws IllegalStateException if it was not possible to insert
- * the element due to capacity restrictions
- * @throws NullPointerException if the specified element is null and this
- * deque does not permit null elements
+ * @return the tail of this deque
+ * @throws NoSuchElementException if this deque is empty
*/
- void addLast(E e);
+ E removeLast();
/**
- * Retrieves and removes the first element of this deque, or
- * null if this deque is empty.
+ * Retrieves and removes the first element of this deque,
+ * or returns {@code null} if this deque is empty.
*
- * @return the first element 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
- * null if this deque is empty.
+ * Retrieves and removes the last element of this deque,
+ * or returns {@code null} if this deque is empty.
*
- * @return the last element 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();
/**
- * Removes and returns the first element of this deque. This method
- * differs from the pollFirst method only in that it throws an
- * exception if this deque is empty.
+ * 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 first element of this deque
+ * @return the head of this deque
* @throws NoSuchElementException if this deque is empty
*/
- E removeFirst();
+ E getFirst();
/**
- * Retrieves and removes the last element of this deque. This method
- * differs from the pollLast method only in that it throws an
- * exception if this deque is empty.
+ * 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 last element of this deque
+ * @return the tail of this deque
* @throws NoSuchElementException if this deque is empty
*/
- E removeLast();
+ E getLast();
/**
* Retrieves, but does not remove, the first element of this deque,
- * returning null if this deque is empty.
+ * or returns {@code null} if this deque is empty.
*
- * @return the first element 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,
- * returning null if this deque is empty.
+ * or returns {@code null} if this deque is empty.
*
- * @return the last element 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();
/**
- * Retrieves, but does not remove, the first element of this
- * deque. This method differs from the peekFirst method only
- * in that it throws an exception if this deque is empty.
- *
- * @return the first element 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 the peekLast method only
- * in that it throws an exception if this deque is empty.
- *
- * @return the last element of this deque
- * @throws NoSuchElementException if this deque is empty
- */
- E getLast();
-
- /**
- * Removes the first occurrence of the specified element in this
- * deque. If the deque does not contain the element, it is
- * unchanged. More formally, removes the first element e
- * such that (o==null ? e==null : o.equals(e)) (if
- * such an element exists).
+ * 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
+ * {@code Objects.equals(o, e)} (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 true if the deque contained the specified element
- * @throws NullPointerException if the specified element is null
+ * @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
+ * deque does not permit null elements
+ * (optional)
*/
boolean removeFirstOccurrence(Object o);
/**
- * Removes the last occurrence of the specified element in this
- * deque. If the deque does not contain the element, it is
- * unchanged. More formally, removes the last element e
- * such that (o==null ? e==null : o.equals(e)) (if
- * such an element exists).
+ * 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
+ * {@code Objects.equals(o, e)} (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 true if the deque contained the specified element
- * @throws NullPointerException if the specified element is null
+ * @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
+ * deque does not permit null elements
+ * (optional)
*/
boolean removeLastOccurrence(Object o);
-
// *** Queue methods ***
/**
* Inserts the specified element into the queue represented by this deque
- * unless it would violate capacity restrictions. In other words, inserts
- * the specified element to the end of this deque. 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.
- *
- * 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 the specified element is null and this
- * deque does not permit null elements
- */
- boolean offer(E e);
-
- /**
- * Inserts the specified element into the queue represented by this
- * deque unless it would violate capacity restrictions. In other words,
- * inserts the specified element as the last element of 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}.
*
* 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
+ * @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
+ * 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);
/**
- * 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.
+ * 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.
*
- * This method is equivalent to {@link #pollFirst()}.
+ * This method is equivalent to {@link #offerLast}.
*
- * @return the first element of this deque, or null if
- * this deque is empty
+ * @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
*/
- E poll();
+ boolean offer(E e);
/**
- * Retrieves and removes the head of the queue represented by this deque.
- * This method differs from the poll method only in that it
+ * 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.
*
* This method is equivalent to {@link #removeFirst()}.
@@ -378,20 +412,22 @@ public interface Deque This method is equivalent to {@link #peekFirst()}.
+ * This method is equivalent to {@link #pollFirst()}.
*
- * @return the head of the queue represented by this deque, or
- * null if this deque is empty
+ * @return the first element of this deque, or {@code null} if
+ * this deque is empty
*/
- E peek();
+ E poll();
/**
* 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 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.
*
* This method is equivalent to {@link #getFirst()}.
*
@@ -400,21 +436,38 @@ public interface Deque 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, inserts the element at the front of this deque unless it would
- * violate capacity restrictions.
+ * 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.
*
* This method is equivalent to {@link #addFirst}.
*
* @param e the element to push
- * @throws IllegalStateException if it was not possible to insert
- * the element due to capacity restrictions
+ * @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
+ * 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);
@@ -425,19 +478,74 @@ public interface 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)
+ * of the stack represented by this deque)
* @throws NoSuchElementException if this deque is empty
*/
E pop();
- // *** Collection Method ***
+ // *** Collection methods ***
/**
- * Returns an iterator over the elements in this deque. The elements
- * will be ordered from first (head) to last (tail).
+ * 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
+ * {@code Objects.equals(o, e)} (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).
*
- * @return an Iterator over the elements in this deque
+ * 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
+ * (optional)
+ * @throws NullPointerException if the specified element is null and this
+ * deque does not permit null elements
+ * (optional)
+ */
+ 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 {@code Objects.equals(o, e)}.
+ *
+ * @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 class of the specified element
+ * is incompatible with this deque
+ * (optional)
+ * @throws NullPointerException if the specified element is null and this
+ * deque does not permit null elements
+ * (optional)
+ */
+ boolean contains(Object o);
+
+ /**
+ * Returns the number of elements in this deque.
+ *
+ * @return the number of elements in this deque
+ */
+ 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