Java Stack Class – Comprehensive Guide to Usage and Methods

Java Stack Class

This tutorial explains Java’s Stack class, its core methods, and practical examples to help you master stack operations.

The Java collections framework includes a Stack class that implements the classic stack data structure. According to the official Java documentation, Stack extends Vector, inheriting all of its methods while adding stack‑specific operations.

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Stack Implementation

A stack follows the Last In, First Out (LIFO) principle: elements are pushed onto the top and popped from the top. The following diagram illustrates this behavior.

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Creating a Stack

To create a stack, import java.util.Stack and instantiate it with the desired generic type:

Stack<Type> stack = new Stack<>();

Examples:

// Integer stack
Stack<Integer> intStack = new Stack<>();

// String stack
Stack<String> stringStack = new Stack<>();

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Stack Methods

Beyond the inherited Vector methods, Stack provides five dedicated operations that distinguish it from generic collections. For a full list of Vector methods, refer to the Vector class documentation.

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push() Method

The push() method adds an element to the top of the stack.

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals = new Stack<>();
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Stack: " + animals);
    }
}

Output

Stack: [Dog, Horse, Cat]

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pop() Method

The pop() method removes and returns the element at the top of the stack.

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals = new Stack<>();
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Initial Stack: " + animals);
        String removed = animals.pop();
        System.out.println("Removed Element: " + removed);
    }
}

Output

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

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peek() Method

The peek() method retrieves the top element without removing it.

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals = new Stack<>();
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Stack: " + animals);
        String top = animals.peek();
        System.out.println("Element at top: " + top);
    }
}

Output

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

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search() Method

The search() method returns the 1‑based position of an element from the top of the stack, or -1 if it’s not present.

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals = new Stack<>();
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Stack: " + animals);
        int pos = animals.search("Horse");
        System.out.println("Position of Horse: " + pos);
    }
}

Output

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

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empty() Method

The empty() method checks whether the stack has any elements.

import java.util.Stack;

class Main {
    public static void main(String[] args) {
        Stack<String> animals = new Stack<>();
        animals.push("Dog");
        animals.push("Horse");
        animals.push("Cat");
        System.out.println("Stack: " + animals);
        boolean isEmpty = animals.empty();
        System.out.println("Is the stack empty? " + isEmpty);
    }
}

Output

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

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Use ArrayDeque Instead of Stack

While Stack implements a stack, it is considered legacy. Modern Java code prefers ArrayDeque (implementing the Deque interface) for stack functionality because it offers better performance and clearer semantics. For more details, see:

• Java ArrayDeque
• Why use Deque over Stack?