Why can't my methods see the parameters being passed to them?
<p>I've been working on Java homework. Here are my instructions:</p>

<blockquote>
  <p>Interface Programming Assignment</p>
  
  <p>Create an interface named ISum.  The interface should define 2 methods.  The first method should take two integers as arguments and return their sum.  The second method should take 2 strings as arguments and return their concatenation.  The second method should be an overloaded version of the first one.</p>
  
  <p>Define another interface named IAverage.  The interface should define one method that takes 2 integer arguments and returns the average.</p>
  
  <p>Create a class named Calculator that implements both the interfaces defined above.  Your class MUST implement exception handling.  Create a driver class that allows a user to call each of the methods in your class.</p>
</blockquote>

<p>My work so far:</p>

<p><code>Main</code> class:</p>

<pre><code>import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Calculator calculatorObject = new Calculator();
        Scanner scannerObject = new Scanner(System.in);

        System.out.println("Enter 1 for integer or 2 for string");
        int test1 = scannerObject.nextInt();

        switch (test1){
            case 1: 
                System.out.println("Enter 1st number");
                int int1 = scannerObject.nextInt();

                System.out.println("Enter 2nd number");
                int int2 = scannerObject.nextInt();   

                System.out.println("Enter 1 for sum or 2 for average");
                int test2 = scannerObject.nextInt(); 

                switch (test2){
                    case 1: 
                        int sum = calculatorObject.intSum(int1,int2);
                        System.out.println("The sum is " + sum);
                        break;

                    case 2:
                        int avg = calculatorObject.intAvg(int1,int2);
                        System.out.println("The avg is " + avg);
                        break;

                    default:
                        System.out.println("You entered an invalid option");    
                        break;    
                }

                break; 

            case 2: 
                System.out.println("Enter 1st string");
                String string1 = scannerObject.nextLine();

                System.out.println("Enter 2nd number");
                String string2 = scannerObject.nextLine();   

                String stringConcat = calculatorObject.stringSum(string1,string2);
                System.out.println("The sum is " + stringConcat);
                break; 

            default:
                System.out.println("You entered an invalid option");    
                break;
        }
    }
} 
</code></pre>

<p><code>ISum</code> interface:</p>

<pre><code>public interface ISum {

    public void intSum();
    public void intAvg();

}
</code></pre>

<p><code>IAverage</code> interface:</p>

<pre><code>public interface IAverage {

    public void intAvg();

}
</code></pre>

<p><code>Calculate</code> class:</p>

<pre><code>abstract class Calculator implements IAverage, ISum { 

    public int intSum (int1,int2){
        int int1;
        int int2;
        int sum = int1 + int2;
        return sum;
    }

    public String stringSum (string1,string2){
        String string1;
        String string2;
        String stringConcat = string1.concat(string2);
        return stringConcat;
    }

    public int intAvg(int1,int2){
        int int1;
        int int2;
        int avg = (int1 + int2)/2;
        return avg;
    }

}
</code></pre>
