Anonymous class

[satya sahu]

Can an anonymous class be declared as implementing an interface and extending a class?
The Answer is :An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.

My question is why can't i declare both?

[Ankit Garg]

that's because the syntax of the Anonymous inner classes doesn't allow you to add an extends or implements clause

so you cannot write something like this

interface TryInterface
{}
 
class TryClass
{}
 
class AnonymousInnerClassTry
{
public static void main(String[] args)
{
TryInterface ti = new TryInterface extends TryClass()
{};
}
}

or like this

interface TryInterface
{}
 
class TryClass
{}
 
class AnonymousInnerClassTry
{
public static void main(String[] args)
{
TryClass tc = new TryClass implements TryInterface()
{};
}
}

I think that's the reason....

[Stephen Davies]

This is perhaps a stab in the dark, but why would you want an anonymous inner class to extend or implement an interface? As an inner class can access members of its outer constituent class, why not extend the class or implement the interface(s) you reqire through the outer class to provide visibility for your inner class.

Just a thought

[Thyagarajan Ramanujam]

Anonymous class already a sub class.(ie) it already has a superclass. In java, a class cant have more than one super class.


For example,

Father son = new Father(){ };

the anonymous class extends Father class. So no further use of extend is possible.

[Stephen Davies]

Thyagarajan:

..is this an example of an anonymous inner class? Your example appears to be simply as a object reference to a Father type named son: Inner classes share more of an internal intimate relationship with their outer class, than an inheritance relationship(though it is indeed inheritance of sorts). I would assume, that inner classes anonymous and non, are a special sort of inheritance, where the outer (containing class) is the holding class rather than a superclass. Also due to the fact that, an instance of the outer class must be made to access the inner class by any sub-classes, suggests a specialized inheritance. I'm not very certain but, is it true that inner classes usually dont have constructors?


However, let me know if I am terribly wrong!

[Campbell Ritchie]

Anonymous classes don't have written constructors; other inner classes can have them.