Question

The Bike and EBike classes are implemented as shown by the code below.

public class Bike
{
  private String make;
  private int numGears;
  private double tirePressure;
  
  public Bike(String m, int g, double t)
  {
    make = m;
    numGears = g;
    tirePressure = t;
  }
  
  public void pumpTire()
  {
    tirePressure += 5.0;
  }
}

public class EBike extends Bike
{
  private int batteryLevel;
  
  public EBike(String m, int g, double t, int b)
  {
    super(m, g, t);
    batteryLevel = b;
  }
  
  public void chargeBattery()
  {
    batteryLevel++;
  }
}

Suppose that the following declarations are made in a separate class.

Bike bike1 = new Bike(“Clasic Cycle”, 16, 65.0);
Bike bike2 = new EBike(“Big EZ”, 8, 72.0, 96);
EBike bike3 = new Bike(“E-xtreme”, 12, 80.0, 44);

Assuming the above three lines compile without error, which of the following statements will cause an error when compiled?

bike3.pumpTire();

bike2.pumpTire();

bike2.chargeBattery();

bike1.pumpTire();

bike3.chargeBattery();

Answer 1

The statement that will cause an error is bike2.chargeBattery().

This is so because bike 2 is an object of class Bike and not EBike ( Bike bike2 = new EBike(“Big EZ”, 8, 72.0, 96) ) and the parent class cannot call the methods of child class ( though the reverse is possible ) . As chargeBattery() is a method of class Ebike so the given statement will throw an error method not found.