Inner classes in java

Answer 1

An inner class is a class within a class:

class MyClass {

class MyInnerClass {

}

}

Inner classes in Java are normally used for things like the nodes of a linked list.

Answer 2

You define an inner class within the curly braces of the outer class:

class ExampleOuterClass {

class ExampleInnerClass { }

}

Piece of cake. And if you compile it,

%javac ExampleOuterClass.java

you'll end up with two class files:

ExampleOuterClass.class

ExampleOuterClass$ExampleInnerClass.class

The inner class is still, in the end, a separate class, so a separate class file is generated for it. But the inner class file isn't accessible to you in the usual way. You can't say

%java ExampleOuterClass$ExampleInnerClass

in hopes of running the main() method of the inner class, because a regular inner class can't have static declarations of any kind. The only way you can access the inner class is through a live instance of the outer class! In other words, only at runtime when there's already an instance of the outer class to tie the inner class instance to.

There are 3 types of Inner Classes:

Answer 3

You define an inner class within the curly braces of the outer class:

class ExampleOuterClass {

class ExampleInnerClass { }

}

Piece of cake. And if you compile it,

%javac ExampleOuterClass.java

you'll end up with two class files:

ExampleOuterClass.class

ExampleOuterClass$ExampleInnerClass.class

The inner class is still, in the end, a separate class, so a separate class file is generated for it. But the inner class file isn't accessible to you in the usual way. You can't say

%java ExampleOuterClass$ExampleInnerClass

in hopes of running the main() method of the inner class, because a regular inner class can't have static declarations of any kind. The only way you can access the inner class is through a live instance of the outer class! In other words, only at runtime when there's already an instance of the outer class to tie the inner class instance to.

There are 3 types of Inner Classes:

• Static

• Method-local

• Anonymous