Java

OOP GUIDE / WORK

STUDENT CLASS 2

Topics

• Implementing the Comparable interface
• Implementing the compareTo method
• Implementing multiple sorting criteria (using a static variable)
• Sorting object arrays with Comparable

TASK – PART 1 – SETUP

Copy and paste the classes Student and Tester from the Student Class Solutions into your IDE.

TASK – PART 2 – SORTING BASED ON A COMPARE MODE

The current version of compareTo compares Student objects based on their grade level.

Now, we want to provide a way to let the programmer sort Student arrays based on grade level, or on last names, or by school.

The solution is fairly simple. We can create a variable called compareMode that keeps track of the desired mode of comparing and then simply organize the compareTo method into multiple parts like below.

public int compareTo(Object o)
{

if (compareMode == 1)
{
//add code to return -1, 0 or 1 based on the compare criteria 1 (grade level)
}

else if (compareMode == 2)
{

//add code to return -1 0 or 1 based on the compare criteria 2 (last name)

}

else

{

//add code to return -1, 0 or 1 based on compare criteria 3 (school)

}

}

Note: Because we only want one compareMode for the entire program, instead of one for every student, we make compareMode a static variable instead of an instance variable. That way, all Student objects will share the one variable.

Make it happen!

TASK – PART 3 – TESTING ALL SORTING CRITERIAS

In the Tester class, sort the array using each criteria. After each sort, output the array to see that it worked.