Question

Having the below code:

    Stack<Integer> integers = new Stack<Integer>();
    Stack<? extends Number> numbers = integers;
    Number n = numbers.pop();
    numbers.push(3);
    numbers.push(n);

I get compilation errors on the last two lines, but although I’ve given it some thought I don’t understand why the compilation errors are there.

The method push(capture#2-of ? extends Number) in the type Stack<capture#2-of ? extends Number> is not applicable for the arguments (int)

When I comment the last line, I still get the above compilation error, but from my understanding the compiler should be able to infer the correct type (Stack) from those lines.

Thanks a lot

Answer 1

very clear answer here
How can I add to List<? extends Number> data structures?