Inner classes allow defining a class within another class. There are several types of inner classes: static nested classes, anonymous inner classes, and local inner classes. Inner classes can access members of the outer class and the outer class can return inner class instances implementing an interface. The main uses of inner classes are event handlers, callbacks, and upcasting inner classes to interfaces or superclasses.

1. Inner Classes Parag Shah Adaptive Software Solutions

2. Agenda What are inner classes Types of inner classes Uses of inner classes

3. What Are Inner Classes An inner class is a class within a class It has access to certain members of the outer class

4. Introduction To Inner Classes Defining an Inner Class public class Outer { public class Inner { public someMethod() {} } } The inner class has access to members of the enclosing class The inner class can be instantiated by another class through it's enclosing class' reference When to use an inner class See [InnerClassesExample.java]

5. Static Nested Classes Defining an Inner Class public class Outer { public static class Inner { public someMethod() {} } } Can access only static members of the enclosing class Can be instantiated without without a reference to the enclosing class When to use static inner classes

6. Anonymous Inner Classes Anonymous inner classes do not have a name public class SoccerDataBuilder { public List parse() { Parser p = new Parser(); p.parse(new Ignorable() { public boolean isValid() { return true; } ); } }

7. Uses of Anonymous Inner Classes Event handlers for UI events The class' main use is to be represented as the interface it implements Ideally have a few lines of code Callbacks See [AnonymousInnerExample.java]

8. Local Inner Classes Inner classes can be defined in methods Very rarely used

9. Inner Classes And Upcasting An inner class can be upcast into an Interface or a super class This is the primary use in anonymous inner classes

10. Private Inner Classes Inner classes can be private Cannot be instantiated from another class The enclosing class can control their instantiation and return them as an implementing interface See [PrivateInnerClass.java]

11. Accessing The Outer Class An inner class can access any attribute or method in the outer class directly An inner class can produce a reference to the outer class by using OuterClassName.this

12. Summary Creating Inner Classes Types of inner classes Accessing outer class elements from an Inner Class