Below is an example of what *not* to do with encapsulation. An IPhone is a Phone which is a Device. Devices already have a field for a Battery. By putting the same field into the IPhone class, it can be confusing when getVoltage() is called.

public class IPhone extends Phone {	
	private Battery b;
	
	public IPhone() {
		b = new Battery(6.0);
		System.out.println(getBattery());
	}
}