We are going to verify that within a given expression, pairs of (round) brackets are matching. E.g. “()()” is correct, but “)(()” isn’t. We need a data structure called “stack” to help us with this task.
A stack has two methods, push() and pop(). Calling push(element) will add the given element to the stack. When calling pop() immediately after that, the element will be returned and removed from the stack. If you try to pop an element from an empty stack, it should throw a NoSuchElementException.
For this particular situation we need a stack of strings to keep track of the history.
- Start with the implementation of the Stack class, with the
push()andpop()methods. You could verify the correctness of your implementation in your application’s main method (of course, if you know how to do it, you should write a test class for JUnit). - Continue with the implementation of the ExpressionValidator class. It has a method
hasMatchingBrackets()which returns a boolean answer, indicating whether the given expression contains only matching brackets. - Bonus assignment: also verify matching square brackets.
- Bonus assignment: make the Stack class a generic class.