AP CSA 3.5 Debugging: Returning Too Soon

Unit 3: Class Creation · Lesson 3.5 · Debugging

Returning Too Soon

Methods: How to Write Them. This is not a blank editor: it is someone else's attempt. Find what is wrong, fix it, and submit to be graded against hidden test cases.

Back to the Lesson 3.5 page All Unit 3 lessons

Why debugging is its own skill

A return statement does not just hand back a value, it ends the method immediately. Put one inside a loop that was supposed to examine every element and the loop becomes a very expensive way of looking at the first item.

What is wrong with it

countAbove returns after examining the very first score, because the return sits inside the loop instead of after it. Move it so the loop finishes first.
allPassing returns true as soon as it sees one passing score. It should return false if ANY score is below the cutoff, and true only if every one passes. Fix the logic so a single failing score decides the answer.
The constructor and getSize are correct.

The program reads

A cutoff, then a count of scores, then that many scores.

The program should print

Three lines: how many scores are strictly above the cutoff, whether every score is at least the cutoff, and how many scores there are.

Worked examples

These show what the FIXED program should print. There are more cases you cannot see, and they use different values, so patching around just these numbers will fail.

Example 1 input

70 5
90 65 80 72 60

Example 1 output

3
false
5

Example 2 input

50 3
50 50 50

Example 2 output

0
true
3

Your answer

Main.java

public class Scores {
  private int[] values;

  public Scores(int[] values) {
    this.values = values;
  }

  public int getSize() {
    return values.length;
  }

  public int countAbove(int cutoff) {
    int count = 0;
    for (int i = 0; i < values.length; i++) {
      if (values[i] > cutoff) {
        count++;
      }
      return count;
    }
    return count;
  }

  public boolean allPassing(int cutoff) {
    for (int i = 0; i < values.length; i++) {
      if (values[i] >= cutoff) {
        return true;
      }
    }
    return false;
  }
}

Input for the Run button

Run sends whatever is in the code box below, bugs and all, so you can see the crash or the wrong answer for yourself before you fix anything.

Stuck?

Hint 1

A counting loop returns AFTER the loop. A searching loop can return from inside, but only when finding one example settles the question for good. Ask which kind each method is before you decide where the return goes.

Hint 2

For a claim about EVERY element, one counterexample is enough to say false, but no single example is ever enough to say true. So the early return inside the loop must be the false one, and true comes after the loop survives every element.

Hint 3

The starter version of allPassing returns true for a list where only the first score passes. Test that case by hand and the logic error is obvious.

Where to go next

Rework the Lesson 3.5 page Try the from-scratch version of this lesson

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