In this lab you will explore some aspects of inheritance in Java. In the first part, you will refactor a provided solution which implements a simple calculator to gain experience with inheritance. In the second part, you will explore the notion of "equality" in Java.

• To explore the the use of inheritence

• To practice recognizing when classes share data or similar methods and how to use inheritence to make these relationships explicit

Retrieve the files provided for this lab here:

In the calculator directory is a solution for a simple calculator (with support for variables). For this part of the lab you will modify this solution to refactor common functionality out of some of the classes into a common class.

Many of the expressions are what we would typically call binary expressions. In particular, AddExpression, DivideExpression, MultiplyExpression, and SubtractExpression each have very similar behavior. To see this clearly, compare AddExpression.java and SubtractExpression.java. In fact, let's compare them using diff to see just how similar they are.

diff AddExpression.java SubtractExpression.java

To refactor this common behavior, follow the steps below.

• Create a new class named BinaryExpression. This class should inherit from Expression.
• Each of the classes listed above must be modified to inherit from BinaryExpression.
• Now lift the common data out of these subclasses into the common parent class BinaryExpression. Make this data private.
• With the common data in the parent, the common functionality will also be lifted. Move the evaluate and toString methods into the BinaryExpression class.
• Add an additional argument to the BinaryExpression constructor. Modify the subclasses to pass a String, representing the operator, to the parent class . Update BinaryExpression's toString to use this operator string.
• Modify the code in evaluate in the BinaryExpression class to evaluate each operand (i.e., lft and rht) and to pass the results to a new, protected method named _applyOperator. This new method will not be defined in BinaryExpression, but must be declared (what sort of method is this?). In each subclass, implement this new method as is appropriate for the subclass's operator.

Examine the provided files in the equality directory.

For this part, you must implement equals and hashCode for the appropriate objects in order for all test cases to pass.

For the CourseSection class, you must implement equals and hashCode in long form (i.e., you must program all computations explicitly). Be sure to handle null values.

For the Student class, you must implement equals and hashCode using the appropriate methods of java.util.Objects.

This lab is due in approximately a week and a half (either Wednesday 11/1 or Thursday 11/2, depending on your section).

Be sure to commit the code by the due date. Your instructor reserves the right to run further tests on your code. Demonstrate your working program to your instructor. Be prepared to show your source code. (Partial credit available up to instructor discretion).