Methods

Stacks

A stack is similar to a queue. The only difference are the method names and the manner in which we retrieve the items.

Before we create a stack, we will have to import the stack class. To make life easier, we can use a * instead to import all classes in the library. It will look something like this.

// This will import stack, among other classes
import java.util.*;

There are several methods to use on a stack. If you are interested, you may search the internet for more information about these methods. However, we are only going to explain the most important methods for now: push(), peek(), and pop().

Creating a Stack

Stack driver = new Stack();

Adding Elements

In order to add an element to the stack, we can use the push() method. This push() operation place the element at the top of the stack.

push(1);
push(2);
push(3);

// Creates a stack with elements [3, 2, 1]

Accessing Elements

To retrieve or fetch the first element of the stack or the element present at the top of the stack, we can use the peek() method. The element retrieved does not get deleted or removed from the stack.

stack.peek();

// Returns 3
// Stack contains [3, 2, 1]

Removing Elements

To remove an element from the stack, we can use the pop() method. The element is popped and removed from the top of the stack.

stack.pop();

// Returns 3
// Stack contains [2, 1]

With these three methods in mind, let’s go ahead and take a look at an example.

import java.util.*;
public class Driver {
    public static void main(String []args) {
        // Default initialization of Stack 
        Stack stack = new Stack(); 
  
        // pushing the elements 
        stack.push("Burger King"); 
        stack.push("Subway"); 
        stack.push("Jack in the Box"); 
  
        // Printing the Stack Elements 
        System.out.println(stack); 
    }
}

Output:

["Jack in the Box", "Subway", "Burger King"]