Stack Class

The Stack Class in Java

The Stack class is a legacy implementation of a Last-In-First-Out (LIFO) stack in Java. It extends the Vector class and provides additional methods for stack-specific operations such as push, pop, and peek. While it is still part of the Java API, its usage is generally discouraged in favor of modern alternatives like Deque implementations (e.g., ArrayDeque).

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Key Characteristics of Stack

• LIFO Behavior: Last element inserted is the first one removed.
• Legacy Implementation: Introduced in Java 1.0.
• Thread Safety: Inherits synchronization from Vector.
• Limited Versatility compared to modern collections.

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Common Use Cases

• Expression parsing
• Backtracking algorithms
• Undo/redo functionality
• Legacy systems using Stack

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Important Methods

Method Description

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E push(E item) Push element to top E pop() Remove and return top E peek() View top element boolean empty() Check if stack empty int search(Object o) Returns position of element

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Example 1: Basic Stack Operations

import java.util.Stack;

public class StackExample {

    public static void main(String[] args) {

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

        stack.push("Apple");
        stack.push("Banana");
        stack.push("Cherry");

        System.out.println("Stack: " + stack);

        System.out.println("Top element: " + stack.peek());

        System.out.println("Popped: " + stack.pop());
        System.out.println("Popped: " + stack.pop());

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

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Example 2: Searching an Element

import java.util.Stack;

public class StackSearchExample {

    public static void main(String[] args) {

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

        stack.push("Apple");
        stack.push("Banana");
        stack.push("Cherry");

        int position = stack.search("Apple");

        System.out.println("Position of Apple: " + position);
    }
}

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Example 3: Checking if Stack is Empty

import java.util.Stack;

public class StackEmptyExample {

    public static void main(String[] args) {

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

        System.out.println("Is stack empty? " + stack.empty());

        stack.push("Apple");

        System.out.println("Is stack empty? " + stack.empty());
    }
}

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Performance Characteristics

Operation	Complexity
push()	O(1)
pop()	O(1)
peek()	O(1)
search()	O(n)

Synchronization overhead can make it slower than modern alternatives.

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When to Use Stack

Use Stack when:

• Maintaining legacy systems
• Explicit synchronized stack behavior required

Prefer modern alternatives:

• ArrayDeque
• Deque interface

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Stack vs ArrayDeque

Feature	Stack	ArrayDeque
Data Structure	Vector-based array	Resizable deque
Thread Safety	Synchronized	Not synchronized
Performance	Slower	Faster
Versatility	Stack only	Stack + Queue + Deque