Question:
(a) Explain the importance of abstract classes in Java with an appropriate example.
(b) Explain what is meant by an interface in Java? Use a simple example to illustrate your answer.
(c) A GUI may contain text-fields, buttons, and other labels. A button usually triggers an event on the GUI. Explain the different processes in registering an event and handling the action performed by the button in Java.
(d) Write the code for a GUI which will allow a user to enter two numbers and then compute the product by clicking on a button. The result can be displayed in a text-field or as a label on the GUI.