Certification Summary

After absorbing the material in this chapter, you should be familiar with some of the nuances of the Java language. You may also be experiencing confusion around why you ever wanted to take this exam in the first place. That's normal at this point. If you hear yourself saying, "What was I thinking?" just lie down until it passes. We would like to tell you that it gets easier…that this was the toughest chapter and it's all downhill from here…

Let's briefly review what you'll need to know for the exam.

There will be many questions dealing with keywords indirectly, so be sure you can identify which are keywords and which aren't.

Although naming conventions like the use of camelCase won't be on the exam directly, you will need to understand the basics of JavaBeans naming, which uses camelCase.

You need to understand the rules associated with creating legal identifiers, and the rules associated with source code declarations, including the use of package and import statements.

You now have a good understanding of access control as it relates to classes, methods, and variables. You've looked at how access modifiers (public, protected, and private) define the access control of a class or member.

You learned that abstract classes can contain both abstract and nonabstract methods, but that if even a single method is marked abstract, the class must be marked abstract. Don't forget that a concrete (nonabstract) subclass of an abstract class must provide implementations for all the abstract methods of the superclass, but that an abstract class does not have to implement the abstract methods from its superclass. An abstract subclass can "pass the buck" to the first concrete subclass.

We covered interface implementation. Remember that interfaces can extend another interface (even multiple interfaces), and that any class that implements an interface must implement all methods from all the interfaces in the inheritance tree of the interface the class is implementing.

You've also looked at the other modifiers including static, final, abstract, synchronized, and so on. You've learned how some modifiers can never be combined in a declaration, such as mixing abstract with either final or private.

Keep in mind that there are no final objects in Java. A reference variable marked final can never be changed, but the object it refers to can be modified. You've seen that final applied to methods means a subclass can't override them, and when applied to a class, the final class can't be subclassed.

Remember that as of Java 5, methods can be declared with a var-arg parameter (which can take from zero to many arguments of the declared type), but that you can have only one var-arg per method, and it must be the method's last parameter.

Make sure you're familiar with the relative sizes of the numeric primitives. Remember that while the values of non-final variables can change, a reference variable's type can never change.

You also learned that arrays are objects that contain many variables of the same type. Arrays can also contain other arrays.

Remember what you've learned about static variables and methods, especially that static members are per-class as opposed to per-instance. Don't forget that a static method can't directly access an instance variable from the class it's in, because it doesn't have an explicit reference to any particular instance of the class.

Finally, we covered a feature new to Java 5, enums. An enum is a much safer and more flexible way to implement constants than was possible in earlier versions of Java. Because they are a special kind of class, enums can be declared very simply, or they can be quite complex—including such attributes as methods, variables, constructors, and a special type of inner class called a constant specific class body.

Before you hurl yourself at the practice test, spend some time with the following optimistically named "Two-Minute Drill." Come back to this particular drill often, as you work through this book and especially when you're doing that last-minute cramming. Because—and here's the advice you wished your mother had given you before you left for college—it's not what you know, it's when you know it.

For the exam, knowing what you can't do with the Java language is just as important as knowing what you can do. Give the sample questions a try! They're very similar to the difficulty and structure of the real exam questions, and should be an eye opener for how difficult the exam can be. Don't worry if you get a lot of them wrong. If you find a topic that you are weak in, spend more time reviewing and studying. Many programmers need two or three serious passes through a chapter (or an individual objective) before they can answer the questions confidently.