cs2381 Notes: 03 Designing Methods

Startup

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• Announce Lab01 extension to Tuesday:
  • Lab software issues.
  • No tutoring on Labor Day.
• Delay attendence until after the first example.

Design Recipe for a Method

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To design a method, follow the design recipe:

• Stub method
  • Name, return type, argument names with types, static?
  • Trivial return statement if needed
• Javadoc
  • Purpose statement
  • @param lines
  • @return line
• Examples
  • Based on the problem statement, write one or more examples
• Initial Tests
  • Translate the examples into tests
• Template
  • Based on the arguments to your method, figure out what you have to work with and write that down.
• Write the function body
• More tests
  • Add tests that exercize any code in the function body that isn’t covered yet.
  • Add tests for edge cases.

Example problem

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In the course syllabus, it gives a mapping from percentage scores to letter grades. An F is a failing grade, while any other grade passes.

Design a static method called passingScore that takes a percentage score as a floating point number and returns a boolean value indicating whether that score would pass the class.

We’ll start with the demo starter from the course website.

Stub method

// In new file main/.../Prob.java

// public class Prob {

static boolean passingScore(float score) {
    return false;
}

Javadoc

/**
 * Is this a passing score?
 *
 * @param  score  The percentage score, typically from 0.0 to 100.0
 * @return        True for a passing score, else false.
 */

Examples

// 75.0 => true
// 30.7 => false

Initial Tests

// In test/.../ProbShould.java

import static demo.Prob.passingScore;

public class ProbShould {

    @Test
    void determine_if_scores_pass() {
        assertEquals(passingScore(85.0f), true);
        assertEquals(passingScore(27.3f), false);
    }

Template

What do we have access to in this function body?

• The arguments
• “this”, if the method isn’t static

static boolean passingScore(float score) {
   ... score ...
}

Body

Pull up the course syllabus to find the pass threshold.

Note: Generally want no top level “if” in boolean function.

static boolean passingScore(float score) {
    return score > 60;
}

More Tests

    void determine_if_scores_pass() {
        assertEquals(passingScore(85.0f), true);
        assertEquals(passingScore(27.3f), false);
        // edge case
        assertEquals(passingScore(60.0f), true);
    }

Run the tests. Fix the bug.