Inner class inheritance

[Sajan Joseph]

-When you inherit from a superclass, do you inherit the inner class?
-When you inherit from a superclass, do you inherit the super class's public static void main() method?
-During instantiation of a sub class, the super class constructor is called first. If the super class has a static inner class, then will this inner class be initialized before the before the super class state is initialized?
SJ

[bill bozeman]

Best way to check these is with some code. So that is what I wrote up for you.
Let me give you the answers to what I found, and then I would copy the code and play with it to see what you get.
1. You don't really inherit innerclasses becuase in order to access the innerclass you have to have an instance of it. But as the code below shows, if you have an instance of the sub class, you can use that instance to create an instance of the inner class.
2. Run Sub.java after you compile this and you will see that you get Parents main method, so yes you do inherit the main method.
3. After you run the code below you will see that the Parent's constrctor is called and then the Sub's, but not the inner class. Inner classes are just like other classes and constructors are not called untile you instantiate it.
Hope this helps,

class Parent
{
    public Parent()
    {
        System.out.println( "I am the constructor for Parent" );
    }
    
    public void aMethod()
    {
        System.out.println( "I am in Parent's aMethod()" );
    }
    
    class ParentInner
    {
        public void innerMethod()
        {
            System.out.println( "I am in innerMethod()" );
        }
    }
    
    static class ParentStaticInner
    {
        public ParentStaticInner()
        {
            System.out.println( "I am the constructor for class inner" );
        }
    }
    
    public static void main( String[] args )
    {
        System.out.println( "I am main from Parent" );
    }
}
class Sub extends Parent
{
    public Sub()
    {
        System.out.println( "I am the constructor for Sub" );
    }
    public void bMethod()
    {
        System.out.println( "I am in Sub's bMethod()" );
    }
}
class TestSub
{
    public static void main( String[] args) 
    {
        Sub s = new Sub();
        s.aMethod();
        s.bMethod();
        //s.innerMethod();  will throw an error
        s.new ParentInner().innerMethod();
    }
}

Bill

[Sajan Joseph]

Thank You Bill,
I ran your code and this is what I understood :
1. A sub class can create an object of the inner class of its superclass.
2.Super class static innerclass is not instantiated automatically. You have to explicitly create an instance of it, before calling any of its methods.
3. and public static void main() is just like any other method inherited by the subclass. But will not be very useful unless it is overridden by the subclass.
Can you tell me the practical uses of inner classes. Do we ever use them? In fact they seem too complicated. When do we use them. What is the use of static inner classes? I am not very clear on the subject. It would be a great help if you can elucidate. I have gone through TIJ. I have a vague idea. But using an inner class in the classes I write, does not come naturally to me. Nor can I think up any particular use of them.
Thanks and regards,
SJ

[Rebecca Mathew]

Sajan, inorder to understand inner classes better, why don't you read...."Getting in touch with your inner class", at the campfire stories(the link is on the Javaranch homepage). It's a wonderful story, and I understood inner classes a lot better after reading it .
Hope this helps
Rebecca