Create Deque_Learn.java

Author: tridibsamanta

Deque_Learn.java

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+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Deque;
+import java.util.Iterator;
+
+/*
+ * A deque (double-ended queue) functions as queues (first-in, first-out) or 
+ * as stacks (last-in, first-out).
+ */
+
+public class Deque_Learn {
+
+	public static void main(String[] args) {
+
+		/*
+		 * The 'Deque' interface extends 'Queue' interface and declares the behaviour of
+		 * a double-ended queue. 'Deque' being an interface needs a class which provides
+		 * implementation to its methods and also that we can create objects of that
+		 * class. 'ArrayDeque' class is used used while creating a deque object.
+		 * 
+		 * The 'ArrayDeque' class extends 'AbstractCollection' class and implements the
+		 * 'Deque' interface. 'ArrayDeque' creates a dynamic array and has no capacity
+		 * restrictions.
+		 */
+
+		Deque<Integer> demoDeque = new ArrayDeque<>();
+
+		/*
+		 * Adding elements to deque
+		 * 
+		 * boolean add(E obj) : Declared in the Collection interface. Adds object to the
+		 * collection. Returns true if object was added, otherwise returns false.
+		 * 
+		 * boolean offer(E obj) : Declared in the Queue interface. Adds object to the
+		 * queue. Returns true if object was added, otherwise returns false.
+		 * 
+		 * void addFirst(E obj) : Declared in the Deque interface. Adds obj to the head
+		 * of the deque. Throws an IllegalStateException if a capacity-restricted deque
+		 * is out of space.
+		 * 
+		 * void addLast(E obj) : Declared in the Deque interface. Adds obj to the tail
+		 * of the deque. Throws an IllegalStateException if a capacity-restricted deque
+		 * is out of space.
+		 * 
+		 * boolean offerFirst(E obj) : Declared in the Deque interface. Attempts to add
+		 * obj to the head of the deque. Returns true if obj was added and false
+		 * otherwise.
+		 * 
+		 * boolean offerLast(E obj) : Declared in the Deque interface. Attempts to add
+		 * obj to the tail of the deque. Returns true if obj was added and false
+		 * otherwise.
+		 * 
+		 * void push(E obj) : Declared in the Deque interface. Adds obj to the head of
+		 * the deque. Throws an IllegalStateException if a capacity-restricted deque is
+		 * out of space.
+		 */
+
+		demoDeque.add(10);
+		// demoDeque = [10]
+
+		demoDeque.offer(20);
+		// demoDeque = [10, 20]
+
+		demoDeque.addFirst(30);
+		// demoDeque = [30, 10, 20]
+
+		demoDeque.addLast(40);
+		// demoDeque = [30, 10, 20, 40]
+
+		demoDeque.offerFirst(50);
+		// demoDeque = [50, 30, 10, 20, 40]
+
+		demoDeque.offerLast(60);
+		// demoDeque = [50, 30, 10, 20, 40, 60]
+
+		demoDeque.push(70);
+		// demoDeque = [70, 50, 30, 10, 20, 40, 60]
+
+		System.out.println("demoDeque = " + demoDeque); // demoDeque = [70, 50, 30, 10, 20, 40, 60]
+
+		/*
+		 * Removing elements from deque
+		 * 
+		 * E remove() : Declared in the Queue interface. Removes the element at the head
+		 * of the queue returning the element in the process. It throws
+		 * NoSuchElementException if the queue is empty.
+		 * 
+		 * boolean remove(Object obj) : Declared in the Collection interface. Removes
+		 * one instance of obj from the queue. Returns true if the element was removed.
+		 * Otherwise, returns false.
+		 * 
+		 * E removeFirst() : Declared in the Deque interface. Removes the element at the
+		 * head of the deque returning the element in the process. It throws
+		 * NoSuchElementException if the deque is empty.
+		 * 
+		 * E removeLast() : Declared in the Deque interface. Removes the element at the
+		 * tail of the deque returning the element in the process. It throws
+		 * NoSuchElementException if the deque is empty.
+		 * 
+		 * boolean removeFirstOccurrence(Object obj) : Declared in the Deque interface.
+		 * Removes the first occurrence of obj from the deque. Returns true if
+		 * successful and false if the deque did not contain obj.
+		 * 
+		 * boolean removeLastOccurrence(Object obj) : Declared in the Deque interface.
+		 * Removes the last occurrence of obj from the deque. Returns true if successful
+		 * and false if the deque did not contain obj.
+		 */
+
+		// demoDeque = [70, 50, 30, 10, 20, 40, 60]
+		demoDeque.remove();
+		// demoDeque = [50, 30, 10, 20, 40, 60]
+
+		demoDeque.remove(10);
+		// demoDeque = [50, 30, 20, 40, 60]
+
+		demoDeque.removeFirst();
+		// demoDeque = [30, 20, 40, 60]
+
+		demoDeque.removeLast();
+		// demoDeque = [30, 20, 40]
+
+		demoDeque.addLast(20);
+		// demoDeque = [30, 20, 40, 20]
+
+		demoDeque.removeFirstOccurrence(20);
+		// demoDeque = [30, 40, 20]
+
+		demoDeque.addFirst(20);
+		// demoDeque = [20, 30, 40, 20]
+
+		demoDeque.removeLastOccurrence(20);
+		// demoDeque = [20, 30, 40]
+
+		System.out.println("demoDeque = " + demoDeque); // demoDeque = [20, 30, 40]
+
+		/*
+		 * Get the head / tail element of deque
+		 * 
+		 * E peek() : Declared in the Queue interface. Returns the element at the head
+		 * of the queue. It returns null if the queue is empty.
+		 * 
+		 * E peekFirst() : Declared in the Deque interface. Returns the element at the
+		 * head of the deque. It returns null if the deque is empty. The object is not
+		 * removed.
+		 * 
+		 * E peekLast() : Declared in the Deque interface. Returns the element at the
+		 * tail of the deque. It returns null if the deque is empty. The object is not
+		 * removed.
+		 * 
+		 * E getFirst() : Declared in the Deque interface. Returns the first element in
+		 * the deque. The object is not removed from the deque. It throws
+		 * NoSuchElementException if the deque is empty.
+		 * 
+		 * E getLast() : Declared in the Deque interface. Returns the last element in
+		 * the deque. The object is not removed from the deque. It throws
+		 * NoSuchElementException if the deque is empty.
+		 */
+
+		// demoDeque = [20, 30, 40]
+		int headElement = demoDeque.peek();
+
+		System.out.println("headElement = " + headElement); // headElement = 20
+
+		headElement = demoDeque.peekFirst();
+
+		System.out.println("headElement = " + headElement); // headElement = 20
+
+		int tailElement = demoDeque.peekLast();
+
+		System.out.println("tailElement = " + tailElement); // tailElement = 40
+
+		headElement = demoDeque.getFirst();
+
+		System.out.println("headElement = " + headElement); // headElement = 20
+
+		tailElement = demoDeque.getLast();
+
+		System.out.println("tailElement = " + tailElement); // tailElement = 40
+
+		/*
+		 * Get & remove the head / tail element of deque
+		 * 
+		 * E poll() : Declared in the Queue interface. Returns the element at the head
+		 * of the queue, removing the element in the process. It returns null if the
+		 * queue is empty.
+		 * 
+		 * E pop() : Declared in the Deque interface. Returns the element at the head of
+		 * the deque, removing it in the process. It throws NoSuchElementException if
+		 * the deque is empty.
+		 * 
+		 * E pollFirst() : Declared in the Deque interface. Returns the element at the
+		 * head of the deque, removing the element in the process. It returns null if
+		 * the deque is empty.
+		 * 
+		 * E pollLast() : Declared in the Deque interface. Returns the element at the
+		 * tail of the deque, removing the element in the process. It returns null if
+		 * the deque is empty.
+		 */
+
+		demoDeque.addFirst(10);
+		demoDeque.addLast(50);
+
+		// demoDeque = [10, 20, 30, 40, 50]
+		int removedElement = demoDeque.poll();
+
+		System.out.println("removedElement = " + removedElement); // removedElement = 10
+
+		// demoDeque = [20, 30, 40, 50]
+		removedElement = demoDeque.pop();
+
+		System.out.println("removedElement = " + removedElement); // removedElement = 20
+
+		// demoDeque = [30, 40, 50]
+		removedElement = demoDeque.pollFirst();
+
+		System.out.println("removedElement = " + removedElement); // removedElement = 30
+
+		// demoDeque = [40, 50]
+		removedElement = demoDeque.pollLast();
+
+		System.out.println("removedElement = " + removedElement); // removedElement = 50
+
+		System.out.println("demoDeque = " + demoDeque); // demoDeque = [40]
+
+		/*
+		 * Get the count of elements present in the deque
+		 * 
+		 * int size() : Declared in the Collection interface. Returns the number of
+		 * elements held in the invoking collection.
+		 */
+
+		// demoDeque = [40]
+		int dequeSize = demoDeque.size();
+
+		System.out.println("Size = " + dequeSize); // Size = 1
+
+		/*
+		 * Check if deque is empty or not
+		 * 
+		 * boolean isEmpty() : Declared in the Collection interface. Returns true if the
+		 * invoking collection is empty. Otherwise, returns false.
+		 */
+
+		if (demoDeque.isEmpty())
+			System.out.println("Deque is empty !");
+		else
+			System.out.println("Deque is not empty !");
+
+		/*
+		 * Check if an object is present the deque
+		 * 
+		 * boolean contains(Object obj) : Declared in the Collection interface. Returns
+		 * true if obj is an element of the invoking collection. Otherwise, returns
+		 * false.
+		 */
+
+		int value = 40;
+
+		if (demoDeque.contains(value))
+			System.out.println("Deque contains " + value);
+		else
+			System.out.println("Deque does not contain " + value);
+
+		/*
+		 * Clear the deque
+		 * 
+		 * void clear() : Declared in the Collection interface. Removes all elements
+		 * from the invoking collection.
+		 */
+
+		demoDeque.clear();
+		// demoDeque = []
+
+		System.out.println("demoDeque = " + demoDeque); // demoDeque = []
+
+		/*
+		 * Construct deque from array
+		 */
+
+		String fruits[] = { "apple", "grape", "banana", "orange" };
+
+		Deque<String> fruitDeque = new ArrayDeque<>();
+
+		Collections.addAll(fruitDeque, fruits);
+
+		System.out.println("fruitDeque = " + fruitDeque); // fruitDeque = [apple, grape, banana, orange]
+
+		/*
+		 * Construct array from deque
+		 */
+
+		String fruitArr[] = fruitDeque.toArray(new String[fruitDeque.size()]);
+
+		System.out.println("fruitArr = " + Arrays.toString(fruitArr)); // fruitArr = [apple, grape, banana, orange]
+
+		/*
+		 * Iterating over the contents of a queue
+		 * 
+		 * Iterator<E> iterator() : Declared in the Collection interface. Returns an
+		 * iterator for the invoking collection.
+		 * 
+		 * Iterator<E> descendingIterator() : Declared in the Deque interface. Returns
+		 * an iterator that moves from the tail to the head (reverse iterator) of the
+		 * deque.
+		 */
+
+		Iterator itr = fruitDeque.iterator();
+
+		while (itr.hasNext()) {
+			System.out.print(itr.next() + " ");
+		}
+
+		System.out.println();
+		
+		Iterator reverseItr = fruitDeque.descendingIterator();
+		
+		while (reverseItr.hasNext()) {
+			System.out.print(reverseItr.next() + " ");
+		}
+		
+		System.out.println();
+		
+		// Iterate using for-each loop
+		
+		for (String fruit : fruitDeque) {
+			System.out.print(fruit + " ");
+		}
+		
+	}
+
+}