Solution to 2ffc: Generic stacks
See code at solutions/code/tutorialquestions/question2ffc
Making the solution to question 1486 generic is pretty straightforward: compare the sample solutions.
Some notes: in GenericStackArray<T> you will have a field:
private T[] elements;
In the constructor of GenericStackArray<T> you cannot write:
elements = new E[STACK_LIMIT];
---remember that one of the rules of generics is that it is not permissible to create a new array with generic element type. You can work around this by writing:
elements = (E[])(new Object[STACK_LIMIT]);
i.e., creating a new array that can hold any sort of object, and casting this to the required array type. The compiler does not like this, because in general in the presence of such casts, the type-safety guarantees of generics do not hold. The compiler can issue a warning. You can suppress this warning by adding:
@SuppressWarnings("unchecked")
just before the declaration of the constructor. What's the point of suppressing this warning? It helps ensure that you do not miss other important warnings that are mixed up in a sea of spurious warnings.
The need to cast arrays of objects in this way is the least elegant feature of Java's generics.