Question

In java I have bound of class which is

class A
B extend A
C extend B
D extend C
Therefore, Can I have
AA a = new BB();
AA a = new CC();
AA a = new DD();
AA a = new AA();

Answer 1

The validity of the statements AA a = new BB(), AA a = new CC(), and AA a = new DD() in Java depends on the inheritance relationship of the classes involved. Without the complete hierarchy, we cannot determine the correctness of object instantiation, but the concepts of inheritance dictate that a class can be instantiated into a variable of its superclass.

Step-by-step explanation:

The question pertains to Java inheritance and object instantiation. In Java, a variable of type class AA can hold an object of class AA or any subclass of AA. However, the ability to execute statements like AA a = new BB(); depends on the actual inheritance hierarchy defined in your classes.

If class BB extends AA, then AA a = new BB(); is valid because BB is a subclass of AA. If CC extends AA, then AA a = new CC(); is also valid for the same reason. Similarly, if DD extends AA, AA a = new DD(); would be correct. Finally, AA a = new AA(); is straightforwardly valid as it directly instantiates the class AA.

In your question, it seems like there is an intended hierarchy where AC extends BD, and BD extends C, but without seeing the entire hierarchy including AA, BB, CC, and DD, it's impossible to determine the validity of the instantiation statements completely.

Each statement requires that the right-hand side class extends the left-hand side class, either directly or through a chain of inheritance.