Comparable Interface - Code Reading-Activity

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Title Comparable Interface - Code Reading Activity
Overview Students learn about the Comparable interface in Java by looking at the code of OpenMRS and the actual implementation of the compareTo method in the String class of Java API.
Prerequisite Knowledge Students should be familiar with the String class and string comparison in Java. They should understand the concept of classes and objects.
Learning Objectives Understand the concept and purpose of the Comparable interface. Understand the benefits of defining classes that implement the Comparable interface.


  • This activity could be done as a homework assignment (either done individually or by pairs of students), or as an inclass (lecture or recitation) activity.
  • This activity could be done either early in CS2 course or as a late semester CS1 activity.
  • This activity is designed to use OpenMRS, but there is nothing specific to OpenMRS. The instructor can use any open source project that has sufficient examples of use of Comparable interface.


  1. Go to openMRS-core GitHub repository at and search compareTo
  2. Locate 4 different examples of a call to the compareTo method, for each:
    • specify the filename and the line # on which the call occurs and write the line that contains the call
    • identify the type of the object the method is called on
    • locate the class associated with this datatype and
      • write the header for this class
      • locate the implementation of the compareTo method and
        • identify the parameter type
        • identify the return type
  3. Recall that you have used the compareTo method in the String class. Below is a partial class definition:
 public final class String
   implements, Comparable<String>, CharSequence 


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