Examples of java.util.Deque

java.util.Deque

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 summarized in the following table:

	First Element (Head)		Last Element (Tail)
	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)}
Remove	{@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()}

This interface extends the {@link Queue} interface. When a deque isused 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:

`Queue` Method	Equivalent `Deque` Method
{@link java.util.Queue#add add(e)}	{@link #addLast addLast(e)}
{@link java.util.Queue#offer offer(e)}	{@link #offerLast offerLast(e)}
{@link java.util.Queue#remove remove()}	{@link #removeFirst removeFirst()}
{@link java.util.Queue#poll poll()}	{@link #pollFirst pollFirst()}
{@link java.util.Queue#element element()}	{@link #getFirst getFirst()}
{@link java.util.Queue#peek peek()}	{@link #peek 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:

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 whena deque is used as a queue or a stack; in either case, elements are drawn from the beginning of the deque.

This interface provides two methods to remove interior elements, {@link #removeFirstOccurrence removeFirstOccurrence} and{@link #removeLastOccurrence removeLastOccurrence}.

Unlike the {@link List} interface, this interface does notprovide 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 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 < E> the type of elements held in this collection

        Integer testInt[] = new Integer[100];
        Integer test101 = new Integer(101);
        for (int i = 0; i < testInt.length; i++) {
            testInt[i] = new Integer(i);
        }    
        Deque deque = new ArrayDeque<Integer>();
        Queue<Integer> que = Collections.asLifoQueue(deque);
        for (int i = 0; i < testInt.length; i++) {
            que.add(testInt[i]);
        }        
        assertEquals(100, deque.size());
        assertEquals(100, que.size());
        for (int i = testInt.length-1; i >=0 ; i--) {
            assertEquals(testInt[i], deque.pop());
        }                
        assertEquals(0, deque.size());
        assertEquals(0, que.size());
        for (int i = 0; i < testInt.length; i++) {
            deque.push(testInt[i]);
        }        
        assertEquals(100, deque.size());
        assertEquals(100, que.size());
        Collection col = new LinkedList<Integer>();
        col.add(test101);
        que.addAll(col);
        assertEquals(test101, que.remove());
        for (int i = testInt.length-1; i >=0 ; i--) {
            assertEquals(testInt[i], que.remove());
        }          
        assertEquals(0, deque.size());
        assertEquals(0, que.size());
    }

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        Integer testInt[] = new Integer[100];
        Integer test101 = new Integer(101);
        for (int i = 0; i < testInt.length; i++) {
            testInt[i] = new Integer(i);
        }    
        Deque deque = new ArrayDeque<Integer>();
        Queue<Integer> que = Collections.asLifoQueue(deque);
        for (int i = 0; i < testInt.length; i++) {
            que.add(testInt[i]);
        }        
        SerializationTest.verifySelf(que, new SerializableAssert(){

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        Integer testInt[] = new Integer[100];
        Integer test101 = new Integer(101);
        for (int i = 0; i < testInt.length; i++) {
            testInt[i] = new Integer(i);
        }    
        Deque deque = new ArrayDeque<Integer>();
        Queue<Integer> que = Collections.asLifoQueue(deque);
        for (int i = 0; i < testInt.length; i++) {
            que.add(testInt[i]);
        }        
        Queue deserQue = (Queue)SerializationTester.readObject(que, "serialization/java/util/Collections_asLifoQueue.golden.ser");

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        if (target.isEmpty()) {
            return target;
        }


        Collection<EventBean> beans = (Collection<EventBean>) target;
        Deque queue = new ArrayDeque();
        for (EventBean next : beans) {
            eventsLambda[streamNumLambda] = next;


            Object item = innerExpression.evaluate(eventsLambda, isNewData, context);
            if (item != null) {
                queue.add(item);
            }
        }


        return queue;
    }

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    */
   private Deque getField(int tag) {
      if (tag == 0) {
         throw new IllegalArgumentException("Zero is not a valid tag number");
      }
      Deque field = null;
      if (fields == null) {
         fields = new HashMap<Integer, Deque>();
      } else {
         field = fields.get(tag);
      }

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        if (target.isEmpty()) {
            return target;
        }


        Collection<EventBean> beans = (Collection<EventBean>) target;
        Deque queue = new ArrayDeque();
        for (EventBean next : beans) {
            eventsLambda[streamNumLambda] = next;


            Object item = innerExpression.evaluate(eventsLambda, isNewData, context);
            if (item != null) {
                queue.add(item);
            }
        }


        return queue;
    }

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            return target;
        }


        ObjectArrayEventBean resultEvent = new ObjectArrayEventBean(new Object[1], resultEventType);
        Collection<Object> values = (Collection<Object>) target;
        Deque queue = new ArrayDeque();
        for (Object next : values) {


            resultEvent.getProperties()[0] = next;
            eventsLambda[streamNumLambda] = resultEvent;


            Object item = innerExpression.evaluate(eventsLambda, isNewData, context);
            if (item != null) {
                queue.add(item);
            }
        }


        return queue;
    }

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