Question

How could I (during runtime) decide which type to return from my function?
Is this possible at all?
I think it is but one can never be sure.

Answer 1

Use polymorphism

public interface MyType {
    public void doSomething();
}

public class A implements MyType {
    public void doSomething(){}
}

public class B implements MyType {
    public void doSomething(){}
}

public class MyClass {

    public MyType getData(){
        if ( /* some condition */ ){ return new A(); } 
        return new B();
    }

    public void test(){
        MyType o = this.getData();
        o.doSomething();
    }
}

then simply return type of MyType and call doSomething() directly on that object; ie you don’t need to know whether the returned type is A or B. All you care about is that it implements doSomething. That is the beauty of polymorphism, i.e. no more ugly is, getType, instanceOf (Java), etc.