Session O3: Interfaces and Polymorphism

In a previous laboratory, you examined Java's mechanisms for inheritance in which a subclass automatically inherits all the methods provide by its superclass. In this laboratory you will investigate a related mechanism, Java's interfaces. You will also learn about polymorphism, one of the key attributes of object-oriented programming. The goals of this laboratory are to

• consider a second form of reuse: reuse through polymorphism;
• learn how Java's inheritance mechanism supports this form of reuse;
• investigate Java's interface mechanism, which also supports this form of reuse; and
• compare interfaces and inheritance.

Your instructor will tell you which of the experiments to perform.

Prerequisite skills:

• Objects and classes
• Conditionals
• Inheritance

Required files:

• DateHelper.java
• NewPoint.java
• Point.java
• PointFun.java
• PointPrinter.java
• Printable.java
• SimpleDate.java
• SimpleInput.java
• SimpleOutput.java
• SimpleTime.java