Exercise : Car and Truck revisited practice-it 

public class Car {
   public void m1() {
      System.out.println("car 1");
   }

   public void m2() {
      System.out.println("car 2");
   }

   public String toString() {
      return "vroom";
   }
}

public class Truck extends Car {
   public void m1() {
      System.out.println("truck 1");
   }
    
   public void m2() {
      super.m1();
   }
    
   public String toString() {
      return super.toString() + super.toString();
   }
}

Truck mycar = new Truck();
System.out.println(mycar);    // vroomvroom
mycar.m1();                   // truck 1
mycar.m2();                   // car 1