how to use deque as stack in java?

A Deque (double-ended queue) is a data structure that allows you to add and remove elements from both ends. In Java, the Deque interface extends the Queue interface and provides methods for inserting, removing, and examining elements at both the beginning and the end of the deque.

To use a Deque as a stack in Java, you can follow these steps:

1. Choose an implementation of the Deque interface. Some common implementations of the Deque interface in Java include ArrayDeque and LinkedList. You can choose the implementation based on your specific requirements (e.g. performance, capacity, thread-safety, etc.).

Deque<Integer> stack = new ArrayDeque<>(); // Using an ArrayDeque

2. Use the push method to add elements to the top of the stack. The push method inserts an element at the front of the deque.

stack.push(1); // Stack: [1]
stack.push(2); // Stack: [2, 1]
stack.push(3); // Stack: [3, 2, 1]

3. Use the pop method to remove elements from the top of the stack. The pop method removes and returns the first element of the deque.

int x = stack.pop(); // x is 3, stack is [2, 1]
int y = stack.pop(); // y is 2, stack is [1]

4. Use the peek method to examine the element at the top of the stack without removing it. The peek method returns the first element of the deque, or null if the deque is empty.

int x = stack.peek(); // x is 1, stack is still [1]

5. Use the isEmpty method to check if the stack is empty. The isEmpty method returns true if the deque is empty, and false otherwise.

boolean x = stack.isEmpty(); // x is false
stack.pop();
boolean y = stack.isEmpty(); // y is true

This is a basic example of how you can use a Deque as a stack in Java. You can use the other methods of the Deque interface to perform additional operations on the stack, such as inserting or removing elements from the end of the deque, or iterating over the elements of the deque.

Note that the Deque interface provides several methods that have the same name and functionality as the methods of the Stack class, but the Stack class is now considered to be a legacy class and its use is discouraged. It is recommended to use a Deque instead of a Stack whenever possible.