class Calculo{

    void soma(int num1, int num2){
        System.out.println(num1 + num2);
    }
}

public class Main {

    public static void main(String args[]){

        Calculo cal = new Calculo();
        cal.soma(5, 25);
    }

}

main.java
public class Main {

    public static void main(String[] args) {

        Mobile mobile;
        mobile = (new Mobile());
        mobile.volume = 5;
        mobile.ligado = true;
    }

}

mobile.java
class Mobile {
    public boolean ligado;
    private boolean displayLigado;
    public int volume = 0;


}