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Tips and Study Notes for Sun Certified Java2 Programmer's Exam

Section 6 Overloading, Overriding, Runtime Type, and Object Orientation

State the benefits of encapsulation in object oriented design and write code that implements tightly encapsulated classes and the relationships "is a" and "has a".

Encapsulation means the internal wirings (variables/fields/properties) of the class are not visible outside. Instead, the class provides accessor (getter and setter) methods for the properties it supports. In other words, have private fields and have public setters and getters.

Consider the following declarations:

public class GearBox
{
  public void  shiftGear(int gearNo){ ... }
}
public interface Movable{ }

public class Car implements Movable
{
  private GearBox gb = new GearBox();
}

public class SportsCar extends Car
{
}

In the above situation:

.SportsCar is-a Car ( because SportsCar extends Car )
.Car has-a GearBox ( because Car has a variable of class GearBox )
.SportsCar has-a GearBox ( because SporstCar is a Car and Car has a GearBox )
.Car and SportsCar is-a Movable (because Car implements Movable and SportsCar extends Car) Although, this is strictly an is-like-a relationship but still can be clubbed together with is-arelationship.

Write code to invoke overridden or overloaded methods and parental or overloaded constructors; and describe the effect of invoking these methods.

Points to remember: . Overloaded methods are entirely independent methods. Two overloaded methods behave as if they were two methods with different names. Method name is NOT important, it's the signature (ie. method name + parameterlist) that governs the behavior and overloaded methods have different signatures.

Write code to construct instances of any concrete class including normal top level classes, inner classes, static inner classes, and anonymous inner classes.