Getting Started with Stacks in Java

Getting started with stacks in Java is essential for understanding both basic and advanced programming concepts. A stack is a linear data structure based on the Last-In-First-Out (LIFO) principle, making it ideal for tasks such as undo functionalities, memory management, and expression evaluation in software development. Here’s a structured guide to help you master stacks in Java.

What is a Stack?

A stack is a collection where elements are added and removed only from one end, called the “top.” The most recently added element is the first one to be removed (LIFO).

Stack Class in Java

Java provides a built-in Stack class in the collections framework, located in java.util.Stack. This class supports common stack operations, including push, pop, peek, and search, and is generic—meaning it can store any object type specified in angle brackets.

Creating a Stack

To use the Stack class, import it first:

import java.util.Stack;

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

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

Essential Stack Operations

• push(item): Adds an item to the top of the stack.
• pop(): Removes and returns the item from the top.
• peek(): Returns the item at the top without removing it.
• empty(): Checks if the stack is empty.
• search(item): Returns the 1-based position of an item from the top, or -1 if not found.

Example: Basic Stack Methods

import java.util.Stack;

public class StackExample {
    public static void main(String[] args) {
        Stack<String> stack = new Stack<>();
        stack.push("Java");
        stack.push("Python");
        stack.push("C++");

        // Peek at the top item
        System.out.println("Top item: " + stack.peek());

        // Pop the top item
        stack.pop();

        // Check if stack is empty
        System.out.println("Is stack empty? " + stack.empty());

        // Search for an item
        System.out.println("Position of Java: " + stack.search("Java"));
    }
}

Custom Stack Implementation

You can also write your own stack class using arrays or linked lists for deeper understanding

class Stack {
    private int[] arr;
    private int top;
    private int capacity;

    Stack(int size) {
        arr = new int[size];
        capacity = size;
        top = -1;
    }

    public void push(int x) {
        if (top == capacity - 1) {
            System.out.println("Stack Overflow");
            return;
        }
        arr[++top] = x;
    }

    public int pop() {
        if (top == -1) {
            System.out.println("Stack Underflow");
            return -1;
        }
        return arr[top--];
    }

    public boolean isEmpty() {
        return top == -1;
    }
}

Applications of Stack

• Undo operations in software
• Parentheses matching and syntax checking
• Backtracking in games and algorithms
• Expression evaluation and conversion
• Function call management (call stack)

Best Practices

• Use the built-in Stack class for typical use cases.
• Prefer Deque (ArrayDeque) for stack functionality in performance-critical applications.
• Implement custom stacks to understand the underlying mechanisms.

Getting started with stacks in Java gives you a powerful tool to solve a wide range of programming problems. Understanding stack operations will help you become a more effective developer as you advance in Java and related technologies.​

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