subclass

[ima clark]

Can a class that is not declared public be subclassed? If so are there any restrictions to this?

[Anthony Villanueva]

Assuming we're not talking about inner classes, a class declaration may only have public or "default" accessibility. Either kind can be subclassed.

[ima clark]

thanks

[Wilfried LAURENT]

Either kind can be subclassed.

except if the class is declared final
W.

[Anthony Villanueva]

True enough

[Dirk Schreckmann]

Can a class that is not declared public be subclassed?
As Anthony said, yes.
If so are there any restrictions to this?
Wilfried already pointed out one restriction. Another important one to be aware of concerns the availability (the scope) of the class. If the class is in some package, and the class is declared to be public, then anybody with access to that package can subclass the class. If the class is given default (package) scope, then only classes that are of the same package have access to the class in order to subclass it.
For example, this class

package dirk ;
 
public class SuperClass 
{
    public static void sayHi() 
    {
        System.out.println( "Dirk says Hi" );
    }
}

can be subclassed by any class that has access to the package dirk. This class

package notdirk ;
 
public class SubClass extends dirk.SuperClass 
{
    public static void main( String[] args ) 
    {
        sayHi() ;
    }
}

will compile and run just fine (assuming that the compiler is told where to find the package dirk). If the super class were declared with package level access only:

package dirk ;
 
class SuperClass 
{
    public static void sayHi() 
    {
        System.out.println( "Dirk says Hi" );
    }
}

the compiler would complain when trying to compile SubClass because dirk.SuperClass is not public in dirk; cannot be accessed from outside package. If the subclass were defined to belong to the dirk package

package dirk ;
 
public class SubClass extends SuperClass 
{
    public static void main( String[] args ) 
    {
        sayHi() ;
    }
}

then everybody would be happily compiled and executed again (if one can be happy when executed).