Stack implementation java

Question

Unable to implement stack through this code...

UseStack.java

     class UseStack{
            public static void main(String[] args) {
                Scanner obj = new Scanner(System.in);
                System.out.println("Enter the size of Stack....");
                int n = obj.nextInt();
                Push push = new Push(n);
                Pop pop = new Pop(n);
                while(true){
                    System.out.println("1: Push");
                    System.out.println("2: pop");
                    System.out.println("3: Show");
                    int choice = obj.nextInt();;
                    switch(choice){
                        case 1:
                        push.push();
                        break;
                        case 2:
                        pop.pop();
                        break;
                        case 3:
                        push.show();    
                        break;
                        default:
                        System.out.println("Invalid Option");
                        break;
                    }
                }
            }
        }

Stack.java

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

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

Push.java

class Push extends Stack {
    Push(int size) {
        super(size);
    }

    private static Scanner obj;
    public void push(){
        obj = new Scanner(System.in);
        System.out.println("Enter Value to push...");
        int value = obj.nextInt();
        System.out.println("Value : "+value);
        if(top==capacity-1){
            System.out.println("StackOverflow");
            return;
        }
        else{
            top++;
            System.out.println("Top : "+top);
            arr[top]=value;
            System.out.println("Pushed... "+arr[top]);
        }
    }

    public void show(){
        if(top==-1){
            System.out.println("StackUnderFlow");
            return;
        }
        else{
            System.out.println("Stack Elements : ");
            for(int i=top;i>=0;i--){
                System.out.println(arr[i]+" ");
            }
        }       
    }
}

Pop.java

public class Pop extends Stack {

    Pop(int size) {
        super(size);
    }
    
    public void pop(){
        if(top==-1){
            System.out.println("StackUnderflow-pop");
            return;
        }
        else{
            System.out.println("Top : "+top);
            System.out.println("Poped.. "+arr[top]);
            top--;
        }
    }
    
}

Problem

In this implementation pop() is not working.....

I think for this Pop class needs to extends both Stack and Push classes as so this is not possible in java ,If I'm wrong can anyone help me with this how to resolved it...

Answer 1

pop() is not working because you are using different objects for push and pop.

You don't need to define another class for push and pop, they are operation add those function inside Stack class.

class Stack {
   ... // members and constructor
   public void push(){..}
   public void pop(){..}
   public void show(){..}
}

And create an object of Stack class and use for push, pop and show

Stack s = new Stack(n);
while(true){
    ... 
    switch(choice){
        case 1:
        s.push();
        break;
        case 2:
        s.pop();
        break;
        case 3:
        s.show();    
        break;
        default:
        System.out.println("Invalid Option");
        break;
    }
}