Question

I have an interface Tree and an abstract class RBTree which implements this interface. I also have several classes Tree1…Tree9 which extend this abstract class.

I’ve written a test unit where i want to do something like this:

public void testRandom(RBTree tree){
    for(int i = 0; i < 10; i++){
        rbTree = new Tree1(); //if the tree in the parameter was of instance Tree1
        rbTree = new Tree2(); //if the tree in the parameter was of instance Tree2
        //etc.

        /**
         * do something with rbTree
         */
    }
}

Is it possible to do this without using a chain of if-statements (or a switch) with a lot of instanceof() ?

(note: i can’t change anything about the design, i know it’s not really optimal)

Answer 1

You can use tree.getClass().newInstance().

In case you want to have some more complex logic than instantiation, you would either need the instanceof approach, or better – make each RBTree subclass have a method that performs that logic (and make that method abstract in RBTree)