Nested Classes and Static Nested Classes of Java 2™ Programmer Exam Cram™ 2 (Exam CX-310-035)

The following table shows the types of nested classes( Java 2™ Programmer Exam Cram™ 2 (Exam CX-310-035)):

Types of Nested Classes            Type          Scope                                        Inner
static nested                                     class       member                                     no
inner [non-static]                             class       member                                      yes
local                                                 class           local                                           yes
anonymous                                   class    only the point where it is defined  yes

Nested Classes ( Java 2™ Programmer Exam Cram™ 2 (Exam CX-310-035))

The Java programming language allows you define a class within another class. Such a class is called a nested class and is illustrated here:

class EnclosingClass {
    ...
    class ANestedClass {
        ...
    }
}

You use nested classes to reflect and to enforce the relationship between two classes. You should define a class within another class when the nested class makes sense only in the context of its enclosing class or when it relies on the enclosing class for its function. For example, a text cursor might make sense only in the context of a text component.

Static Nested Classes

A static nested class is declared inside another class and is declared with the static modifier. Like static methods, a static nested class can only refer directly to static variables and methods. It can refer to instance variables and methods only when given a reference to an object of the enclosing class type. The following code is a rough outline of the way a static class is declared:

class NormalClass {
   // static methods and variables
   static class NestedClass {
       // methods and variables of NestedClass
     }
   // instance methods and variables of NormalClass
}

Terms you'll need to understand:

• Nested class
• Inner class
• Member class
• Local class
• Anonymous inner class

final local variable

Question 1 of Java 2™ Programmer Exam Cram™ 2 (Exam CX-310-035)

You need to write code in an applet that will call the submitData method when button1 is clicked. To do this, use addActionListener to connect button1 with an object that implements the ActionListener interface. The only method in this interface has this signature:

void actionPerformed( ActionEvent e );

Which of the following anonymous class declarations is the correct way to do this?

• A.
button1.addActionListener(
       new ActionListener()
       { public void
           actionPerformed( ActionEvent evt )
         {  submitData() ;
         }
       }
     );
• B.
button1.addActionListener(
       new Object implements ActionListener()
       { public void
           actionPerformed( ActionEvent evt )
         {  submitData() ;
         }
       }
     );
• C.
button1.addActionListener(
       new ActionListener()
       { submitData() ;
       }
     );

Answer A is correct. This block of code will call the submitData method when button1 is clicked. Answer B is incorrect because the Object implements terminology is wrong. An anonymous inner class implementing an interface does extend Object, but the compiler provides the default. Answer C is incorrect because it does not have a method declaration for actionPerformed, the method required by the ActionListener interface.
 

Question 2 of Java 2™ Programmer Exam Cram™ 2 (Exam CX-310-035)

Consider the following outline of the declaration of a normal class with an inner class.

public class NormClass {
  public class NestedClass {
       // methods and variables of NestedClass
   }
   // methods and variables of NormClass
}

Which of the following is the correct way for a method inside NestedClass to refer to the enclosing instance of NormClass?

• A. this
• B. NormClass.this
• C. this.NormClass
• D. this.this
• E. this.super
• F. super