Reverse Polish Notation Calculator

Here is my code for what i have done using an array stack.
there are no errors but my program doesn't return the final value when I enter "="
Code java:
import cs2.*;
import java.util.Scanner;
 
public class ArrayStack<T> implements Stack<T>
  {
 
    private T[] data;
 
    private int topIndex;
 
    @SuppressWarnings("unchecked")
    public ArrayStack (int initSize)
      { data = (T[])new Object[initSize];
        topIndex = -1;
      } // Constructor
 
    public ArrayStack ()
      { this(100);
      } // Constructor
 
      public void push (T item)
 
// Push the new item onto an ArrayStack
{ if (topIndex >= data.length-1)
throw new NoSpaceAvailableException();
data[++topIndex] = item;
} // push
 
 
public T pop () // Pop item off top of stack
{ if (topIndex < 0)
throw new EmptyException("stack is empty");
return data[topIndex--];
} // pop
 
public T top () // Return a copy of top item
{ if (topIndex < 0)
throw new EmptyException("stack is empty");
return data[topIndex];
} // top
 
 
public boolean isEmpty ()
// Return TRUE if no items on stack
{ return topIndex < 0;
} // isEmpty
 
//public static double execute(String expr)
 
 
 
 
      	public static void main(String[] args)
      	{
ArrayStack<Double> st = new ArrayStack<>();
 
 
Scanner scan = new Scanner(System.in);
 
 
Object x = scan.next();
 
 
 
 
        while(scan.hasNext())
        {
            if(scan.hasNextDouble())
            {
                    st.push(scan.nextDouble());
            }
            else
            {
 
                double a, b;
 
 
 
                        if (x == '+')
                        {a = st.pop();
                        b = st.pop();
                        st.push(b + a);}
 
                        else if (x == '-')
                        {a = st.pop();
                        b = st.pop();
                        st.push(b - a);}
                        else if (x == '*')
                        {a = st.pop();
                        b = st.pop();
                        st.push(b * a);}
 
 
 
                        else if (x == '/')
                        {a = st.pop();
                        b = st.pop();
                        st.push(b / a);}
 
 
                        else if (x == '=')
                        {st.pop();
                        System.out.print("The answer is" + st.pop());
 
                        }
 
                    }
               }
 
 
 
 
 
      	} //main
 
  }// class ArrayStack