Create DequeDemo.java

rahulXbarnwal · web-flow · commit e13a2c972cd1 · 2026-03-16T01:34:13.000+05:30
diff --git a/src/learnCollections/DequeDemo.java b/src/learnCollections/DequeDemo.java
@@ -0,0 +1,65 @@
+package learnCollections;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.LinkedList;
+
+public class DequeDemo {
+    public static void main(String[] args) {
+        /*
+            INSERTION METHODS
+
+            addFirst(E e) - adds element at the front of the deque, throws exception if deque is full
+            offerFirst(E e) - adds element at the front of the deque, returns false if deque is full
+            addLast(E e) - adds element at the end of the deque, throws exception if deque is full
+            offerLast(E e) - adds element at the end of the deque, returns false if deque is full
+         */
+
+        /*
+            REMOVAL METHODS
+
+            removeFirst() - removes and returns the first element of the deque, throws exception if deque is empty
+            pollFirst() - removes and returns the first element of the deque, returns null if deque is empty
+            removeLast() - removes and returns the last element of the deque, throws exception if deque is empty
+            pollLast() - removes and returns the last element of the deque, returns null if deque is empty
+         */
+
+        /*
+            EXAMINATION METHODS
+
+            getFirst() - retrieves, but does not remove, the first element of the deque, throws exception if deque is empty
+            peekFirst() - retrieves, but does not remove, the first element of the deque, returns null if deque is empty
+            getLast() - retrieves, but does not remove, the last element of the deque, throws exception if deque is empty
+            peekLast() - retrieves, but does not remove, the last element of the deque, returns null if deque is empty
+         */
+
+        /*
+            STACK METHODS (Deque can be used as a stack)
+
+            push(E e) - Adds an element at the front (equivalent to addFirst(E e)). Throws exception if deque is full
+            pop() - Removes and returns the first element (equivalent to removeFirst()), throws exception if deque is empty
+         */
+
+
+        Deque<Integer> deque1 = new ArrayDeque<>(); // faster iteration, low memory, no null allowed
+        // circular array, head and tail pointers
+        // no need to shift elements, just shift head and tail pointers
+        deque1.addFirst(10);
+        deque1.addLast(20);
+        deque1.offerFirst(5);
+        deque1.offerLast(25);
+        System.out.println(deque1); // [5, 10, 20, 25]
+
+        System.out.println("First element: " + deque1.getFirst()); // 5
+        System.out.println("Last element: " + deque1.getLast()); // 25
+        deque1.removeFirst(); // removes 5
+        deque1.pollLast(); // removes 25
+        // Current Deque: [10, 20]
+
+        for(int num: deque1) {
+            System.out.println(num); // 10, 20
+        }
+
+        Deque<Integer> deque2 = new LinkedList<>(); // insertion, deletion somewhere in middle is faster, allows null elements
+    }
+}
