5 Balloons

Stack is a commonly used Data Structure in programming. You can imaging a Programming Stack as similar to any real world stack. A stack of chairs, a stack of cards. What goes inside the stack first comes out last, Or what goes in a stack last comes out first.

Thus an Stack is a Last in First Out (LIFO) Structure of Data

Let’s get familiar with certain programming terms before diving into the implementation. When we put a new data element in a Stack we are doing a push, when we get the element from the stack we are doing a pull, When we are checking the top most element of stack without removing it from stack, its a peek.

Implementation in Java

package info.FiveBalloons.Examples;

import java.util.Arrays;

public class TheStack {
    
    private String[] stackArray;
    private int stackSize;
    private int topOfStack = -1;
    
    TheStack(int stackSize){
        this.stackSize = stackSize;
        stackArray = new String[this.stackSize];
        Arrays.fill(stackArray, "-1");
    }
    
    
    //Push operation
    public void push(String data){
        if(topOfStack +1 < stackSize){
            topOfStack++;
            stackArray[topOfStack] = data;
            System.out.println("PUSH: New data element "+data+" is pushed into stack");
        }else{
            System.out.println("Stack is full");
        }
    }
    
    //Pop Operation
    public String pop(){
        if(topOfStack >= 0){
            System.out.println("POP: top data element "+stackArray[topOfStack]+" is removed from stack");
            stackArray[topOfStack] = "-1";
            return stackArray[topOfStack--];
        }else{
            System.out.println("Sorry but the stack is empty");
            return "-1";
        }
    }
    
 // Peek operation
    public String peek() {
        System.out.println("PEEK: " + stackArray[topOfStack] + " is at the top of the Stack.");
        return stackArray[topOfStack];
    }
    
 // Using our Stack
    public static void main(String[] args ) {
        
        TheStack theStack = new TheStack(10);
        theStack.push("5Balloons");
        theStack.push("Programming");
        theStack.push("Tutorials");
        theStack.peek();
        theStack.pop();
        theStack.pop();
        theStack.pop();
        
    }

}

This program will produce the following output.