Question

Use Java to implement a basic stack using an array of integers. For the stack, you will create an array of integers that holds 5 numbers. To make it easier, you can declare the array at the class level. That way you will be able to use the array in any method in your class without using parameters.

Your input/output interface should look something like the following:

What operation do you want to do?

push

What number do you want to push?

5

5 has been pushed on the stack

What operation do you want to do?

push

Error: Stack is full

What operation do you want to do? pop

The number popped is 5

What operation do you want to do?

pop

Error: Stack is empty

Variations on the wording are acceptable. But the program needs to acknowledge what number has been pushed or popped. Also, when the user tries to push onto a full stack, the program should print an alert, but otherwise not change the stack. Similarly, if the user tries to pop from an empty stack, the program needs to print an alert, but not change the stack. You will need to implement several methods, including: Push , Pop , Stack Full , Stack Empty Depending on how you structure your program, you may need more methods.

Answer 1

Rate my solution and comment if any doubts

Code:

import java.util.*;
public class Stack
{
   //all the variables , arrays and methods are declared as static because
   //they are called by static method main()
   // or else we should create object for every for non static method to use them in static method
   static int max=5;
   // max is the length of the stack
   static int[] stack_arr=new int[max];
   // it is array implementation of stack
   static int top=-1;
   // initilly the stack will be empty so top will be -1
   public static void main(String[] args) {
       // object is created for Scanner class to take input
       Scanner scan=new Scanner(System.in);
       // menu
       System.out.println("Enter your choice(pop,push,print or -1 to exit) \n");
       System.out.print("What operation do you want to do? ");
       // asking input
       String x=scan.nextLine();
       // equals() method return true if the both strings are equal
       // this loop terminate until user enters -1
       while(!x.equals("-1"))
       {
           // if user enters pop then pop() method is called
           if(x.equals("pop"))
           {
               pop();
           }
           // if the user enters push then push() method is called
           else if(x.equals("push"))
           {
               push();
           }
           // if user enters print then print() method is called
           else if(x.equals("print"))
           {
               display();
           }
           // is user enters otherthan push,pop,print then Invalid input is printed
           else
           {
               System.out.println("Invalid Input");
           }

           System.out.print("\nWhat operation do you want to do? ");
           // asking next input
           x=scan.nextLine();
       }
   }
   // this method return true if the stack is full
   // which means the top element is at end of stack
   public static boolean isFull(){
       return top==max-1;
   }
   // this method return true if the stack is empty
   // which means the top is -1
   public static boolean isEmpty(){
       return top==-1;
   }
   // this method will pop the element from stack
   public static void pop()
   {
       // if stack is empty then error message will be displayed
       if(isEmpty()){
           System.out.println("Error: Stack is empty");
       }
       // if the is stack is not empty
       // then top element of stack is stored and top is decremented
       else
       {
           int i=stack_arr[top];
           top--;
           System.out.println("The number popped is "+i);
       }
   }
   // this method will push the element to stack
   public static void push()
   {
       // Scanner object to ask input
       Scanner scan=new Scanner(System.in);
       // if the stack is full then error message wil be displayed
       if(isFull())
       {
           System.out.println("Error: Stack is full");
       }
       // if the stack is not full then it asking for element
       // incrementing the top and storing it in the stack
       else
       {
           System.out.println("What number do you want to push?");
           int i=scan.nextInt();
           stack_arr[++top]=i;
           System.out.println(i+" has been pushed on the stack");
       }
   }
   // this method is used to print the elements in the stack
   public static void display()
   {
       // is stack is empty error message will be displayed
       if(isEmpty())
       {
           System.out.println("Error: Stack is empty");
       }
       // the elements in stack will be displayed
       else
       {
           for(int i=top;i>=0;i--)
           {
               System.out.print(stack_arr[i]+" ");
           }
           System.out.println();
       }
   }
}

Code(Screenshot):

Output(Screenshot):