visual basic barcode printing 8: Inner Classes in Java

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8: Inner Classes
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13. void foof(); 14. } 15. class Bar { 16. void doStuff(Foo f) { } 17. }
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All the action starts on line 4. We re calling doStuff() on a Bar object, but the method takes an instance that IS-A Foo, where Foo is an interface. So we must make both an implementation class and an instance of that class, all right here in the argument to doStuff(). So that s what we do. We write
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new Foo() {
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to start the new class definition for the anonymous class that implements the Foo interface. Foo has a single method to implement, foof(), so on lines 5, 6, and 7 we implement the foof() method. Then on line 8 whoa! more strange syntax appears. The first curly brace closes off the new anonymous class definition. But don t forget that this all happened as part of a method argument, so the close parenthesis ) finishes off the method invocation, and then we must still end the statement that began on line 4, so we end with a semicolon. Study this syntax! You will see anonymous inner classes on the exam, and you ll have to be very, very picky about the way they re closed. If they re argument local, they end like this,
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but if they re just plain old anonymous classes, then they end like this:
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Regardless, the syntax is not what you use in virtually any other part of Java, so be careful. Any question from any part of the exam might involve anonymous inner classes as part of the code.
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CERTIFICATION OBJECTIVE
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Static Nested Classes
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We saved the easiest for last, as a kind of treat : ) You ll sometimes hear static nested classes referred to as top-level nested classes, or static inner classes, but they really aren t inner classes at all, by the standard definition
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Static Nested Classes
of an inner class. While an inner class (regardless of the flavor) enjoys that special relationship with the outer class (or rather the instances of the two classes share a relationship), a static nested class does not. It is simply a non-inner (also called top-level ) class scoped within another. So with static classes it s really more about name-space resolution than about an implicit relationship between the two classes. A static nested class is simply a class that s a static member of the enclosing class, as follows:
class BigOuter { static class Nested { } }
The class itself isn t really static; there s no such thing as a static class. The static modifier in this case says that the nested class is a static member of the outer class. That means it can be accessed, as with other static members, without having an instance of the outer class.
Just as a static method does not have access to the instance variables and methods of the class, a static nested class does not have access to the instance variables and methods of the outer class. Look for static nested classes with code that behaves like a nonstatic (regular inner) class.
Instantiating a Static Nested Class
The syntax for instantiating a static nested class is a little different from a normal inner class, and looks like this:
class BigOuter { static class Nested { } } class Broom { public static void main (String [] args) { BigOuter.Nested n = new BigOuter.Nested(); //Use both class names } }
CERTIFICATION SUMMARY
You re on the home stretch now; just one more chapter follows this one. You ve learned all about inner classes (including static nested classes), and you re aware that they ll show up throughout the exam, regardless of the topic. You re comfortable with
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