I am trying to make a calculator with Java and 3 Classes

Question

I am very new to JAVA Programming and was trying to make a Java Program that consists of 2 classes and an interface. The main class is StartingPoint.java, the other class is Calculate.java and the interface is Equations.java.

So far I have one equation in the Equation.java interface which consists of a simple addition function. I want the program to prompt the user to insert 2 integers and return the added solution. Any help would be greatly appreciated.

This is my main class called StartingPoint.java

import java.util.Scanner;


public class StartingPoint {
public static void main (String Hoda[]){

    System.out.println("Please enter two values");

    Scanner a = new Scanner(System.in);
    Scanner b = new Scanner(System.in);

    Calculate calculator = new Calculate();

    int answer = calculator.add(in.nextInt(a), nextInt(Scanner b));
    System.out.print(answer);
}
}

Here is my second class: Calculate.java

import java.util.Scanner;


public class Calculate implements Equations {



@Override
public int add(Scanner a, Scanner b) {
    // TODO Auto-generated method stub
    return  (a + b);
}

}

And here is my Interface called Equations.java

import java.util.Scanner;



public interface Equations {
int add(Scanner a, Scanner b);
}

Answer 1

You maybe want to convert the values into integer...something like this:

@Override
public int add(Scanner a, Scanner b) {
    int n1=Integer.parseInt(a.next());
    int n2=Integer.parseInt(b.next());
    return  (n1 + n2);
}

I see you are new to java. Take a look at your function:

public int add(...

java expects this function to return an integer. You are returning a + b, but a and b are instances of the object Scanner, not Integers. So we have to "transform" the input string into and integer object. Java is a very high level language, so almost every object has plenty of methods that will help us to do whatever we want. In this case, the class Integer has a static method called parseInt(String args) that will parse the given string and check if it is numeric. If it is numeric, it will return an integer. If not, it will throw an exception. That's why you should validate the input. If you type a non numeric value it will crash.