Java Stack Class

In this tutorial, we will learn about the Java Stack class and its methods with the help of examples.

The Java Collections framework has a class named Stack that provides the functionality of the stack data structure.

The Stack class extends the Vector class.

Java Stack class extending the Vector class


Stack Implementation

In stack, elements are stored and accessed in Last In First Out manner. That is, elements are added to the top of the stack and removed from the top of the stack.

Working of stack data structure


Stack Methods

Since Stack extends the Vector class, it inherits all the methods Vector. To learn about different Vector methods, visit Java Vector Class.

Besides these methods, the Stack class includes 5 more methods that distinguish it from Vector.


push() Method

To add an element to the top of the stack, we use the push() method. For example,

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals= new Stack<>();

        // Add elements to Stack
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");

        System.out.println("Stack: " + animals);
    }
}

Output

Stack: [Dog, Horse, Cat]

pop() Method

To remove an element from the top of the stack, we use the pop() method. For example,

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals= new Stack<>();

        // Add elements to Stack
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Initial Stack: " + animals);

        // Remove element stacks
        String element = animals.pop();
        System.out.println("Removed Element: " + element);
    }
}

Output

Initial Stack: [Dog, Horse, Cat]
Removed Element: Cat

peek() Method

The peek() method returns an object from the top of the stack. For example,

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals= new Stack<>();

        // Add elements to Stack
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Stack: " + animals);

        // Access element from the top
        String element = animals.peek();
        System.out.println("Element at top: " + element);

    }
}

Output

Stack: [Dog, Horse, Cat]
Element at top: Cat

To search an element in the stack, we use the search() method. It returns the position of the element from the top of the stack. For example,

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals= new Stack<>();

        // Add elements to Stack
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Stack: " + animals);

        // Search an element
        int position = animals.search("Horse");
        System.out.println("Position of Horse: " + position);
    }
}

Output

Stack: [Dog, Horse, Cat]
Position of Horse: 2

empty() Method

To check whether a stack is empty or not, we use the empty() method. For example,

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals= new Stack<>();

        // Add elements to Stack
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Stack: " + animals);

        // Check if stack is empty
        boolean result = animals.empty();
        System.out.println("Is the stack empty? " + result);
    }
}

Output

Stack: [Dog, Horse, Cat]
Is the stack empty? false

Use ArrayDeque Instead of Stack

The Stack class provides the direct implementation of the stack data structure. However, it is recommended not to use it. Instead, use the ArrayDeque class (implements the Deque interface) to implement the stack data structure in Java.

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