package com.mycompany.test;

public class Calculator {

	public static void main(String[] args) {
        int a = 4;
		int b = 2;
		System.out.println(sum(a,b));
        System.out.println(minus(a,b));
	}

    private static int sum(int a, int b){
        return a + b;
    }
    
    private static int minus(int a, int b) {
		return a - b;
	}


}

package com.mycompany.test;

public class Calculator {

	public static void main(String[] args) {
        int a = 4;
		int b = 2;
		System.out.println(sum(a,b));
        System.out.println(minus(a,b));
        System.out.println(multi(a,b));
	}

    private static int sum(int a, int b){
        return a + b;
    }

    private static int minus(int a, int b) {
		return a - b;
	}

    private static int multi(int a, int b) {
		return a * b;
	}

}

Add mul function