How to Cast a Vector to Vector i

问题:

I am using JComboBox with a custom class object, and the equals method is over-ridden, and integrated very deeply into the code.

The problem is that if two objects are equal in a JComboBox drop down, then if one is selected all are selected, and the get selected index returns -1.

Is there a ways to cast a Vector<ObjectA> to a Vector<ObjectB>? I tried

Vector<Clas_2> v_temp=(ca.courses.get(i).classes);

and

Vector<Clas_3> v_temp=(ca.courses.get(i).classes);

Where Clas_2 is a parent of Clas_1 and Clas_3 is a extends of Clas_1, but neither of them compile.

All i need is JComboBox not to use the over-ridden equals method.

*Note I know I can cast each individual element into a new array, but would rather have a more memory efficient solution.

回答1:

Changing the type you declare a variable as in code won't change what equals() method is called. It will always be the overriden one, irrespective of what you cast it to. This is how polymorphism works. You'll need to create a different class if you want a different implementation of equals.

回答2:

No, not without being type-unsafe. But you can cast Vector<Clas_1> to Vector<? extends Clas_2> though which should solve your problem.

Since Clas_2 is a parent class of Clas_1, anything you get from a Vector<Clas_1> is an instance of Clas_2, but you cannot add any Clas_2 to a Vector<Clas_1> since not all instances of of Clas_2 are instances of Clas_1. The extends syntax makes that distinction.

回答3:

I agree with Mike. Take a look at this article where the author suggests using an external comparator with some custom code.