数组列表-级别的大小？

Question

As part of my homework I have the following code:

  ArrayList <Integer> marks = new ArrayList();

  Collections.addAll(marks, (Integer.parseInt(markInput.getText())));

  private void analyzeButtonActionPerformed(java.awt.event.ActionEvent evt) 
  {
      analyzeTextArea.setText("Number at level R:" + calculateLevelR());
  }

  private int calculateLevelR() {
      int sum = 0;
      for (Integer mark: marks) {
          if(mark < 50)
              sum += mark;
          sum = marks.size();
      }
      return sum;
  }

When a user enters a set of grades, I'm trying to calculate and display the amount of grades that are "level R" (under 50) but the above code does not work properly, instead it calculates the size of the whole array.

How can I get it to calculate just the amount of grades at "level R"?

Answer 1

Other answers have already pointed out the exact problem, looking at your comments may be a code snippet can explain better. See below

  private int calculateLevelR() {
      int sum = 0;
      for (Integer mark: marks) {
          if(mark < 50)
              sum += mark;
          sum = marks.size(); // If mark is less than 50 add mark to sum else sum = size of arrayList
      }
      return sum;
  }

What you need is :

  private int calculateLevelR() {
      int sum = 0;
      for (Integer mark: marks) {
          if(mark < 50)
              sum++; // If mark is less than 50 increment sum
      }
      return sum; // finally when check all marks return sum, this sum will represent total number of marks less than 50.
  }

Answer 2

Maybe because you have this sum = marks.size(); right after this sum += mark; in your loop.

In addition you should sum grades amount, not value, so you should add just 1 if a mark is under 50 (eg. ++sum ), not the actual mark.

Answer 3

Thats because you are setting sum to marks.size() after the call to sum += mark; Just remove the som= marks.size() line.