How "reject" instancing a class

Question

For example,

public class Test {
    Test() {
    if(xxx)//do some check here
        //reject instancing class test.
    }
}

I think I can throw a exception to reject it, is there any other way? I am not sure what's the effect of instancing been rejected, but I think a natural way is:

Test test = new Test();//return null here indicating instancing rejected.

I expect java and C++ all should have this "reject" feature.

Answer 1

If you want to return null you could get use of Factory pattern. E.g. instead of Test test = new Test(); you could write Test test = TestFactory.CreateTest();, and implement all the checks you need in TestFactory.CreateTest.

new Test() always returns a non-null instance of Test (at least in Java).

Answer 2

You can't return null from a constructor, but you can (as you suggest) throw an exception.