Question

I have a problem trying to insert a calculated result into an ArrayList of Student’s list of results.

It goes like this.

1. An ArrayList (called FullList) holds a list of Student objects.
2. A Student object has a name (as a String) and a resultslist (as an ArrayList).
3. When i receive a Result object, it comes with a name (as a String) and result (as a Integer).
4. I want to insert this Result object into the Student object’s resultlist.
5. However, the student names are not defined upfront but deduced upon the receipt of a Results object.
6. That is to say, if there is no Student object in FullList, the Result object will trigger the creation of a Student object and insert itself into the Student object’s resultslist.
   Then the created Student object will be inserted into FullList.

I have written the code below but I’m getting multiple insertions of the same tag into FullList instead of insertion of multiple results into each tag.

Q1: I can’t figure out what’s wrong! Need a mind prick from the Gurus!
Q2: I will be using the following code for up to 90,000 students. Is this a feasible way of housing student results?

class Result {
   String name;
   int result;

   public Result(String name, int result) {
      this.name = name;
      this.result = result;
   }

   /* start - Getting hungup over this method
    *         Something is wrong here and i don't know what it is
    */
   public void setResult(ArrayList <Student> fullList) {

      for (Student s : fullList) {
         if (s.getName().equalsIgnoreCase(this.name)) {
            s.setResult(this);
         }
         else {         /* enters here if Student does not exist in fullList */
            Student s = new Student(this.name); /* create new student */
            s.setResult(this);                  /* insert result into Student's resultslist */
            fullList.add(s);                    /* add Student into fullList */
         }
      }
   }
   /* end */

   public String getName() {
      return this.name;
   }
}

class Student {
   String name;
   ArrayList <Result> resultslist;

   public Student(String name) {
      this.name = name;
      resultslist = new ArrayList <Result> ();
   }

   public void setResult(Result result) {
      this.resultslist.add(result);
   }

   public String getName() {
      return this.name;
   }
}

class StudentResults {

   public static void main (String [] args) {

      ArrayList <Student> FullList = new ArrayList <Student> ();

      Result r1 = new Result("John", 12);
      Result r2 = new Result("Jamie", 99);
      Result r3 = new Result("John", 69);
      Result r4 = new Result("Jacque", 56);
      Result r5 = new Result("Jacque", 100);
      Result r6 = new Result("Jamie", 100);

      r1.setResult(FullList);
      r2.setResult(FullList);
      r3.setResult(FullList);
      r4.setResult(FullList);
      r5.setResult(FullList);
      r6.setResult(FullList);

   }
}

Answer 1

For each student in the list, you’re inserting a new student if this student doesn’t have the same name as the result to insert:

for (Student s : fullList) {
     if (s.getName().equalsIgnoreCase(this.name)) { // current student has same name as result
         s.setResult(this);
     }
     else { // current student doesn't have the same name as result
        Student s = new Student(this.name); 
        s.setResult(this);
        fullList.add(s);
     }
}

The above should be written as:

Student s = findStudentWithName(fullList, this.name);
if (s == null) {
    Student s = new Student(this.name); 
    s.setResult(this);
    fullList.add(s);
}
else {
    s.setResult(this);
}

And the findStudentWithName method would look like this:

private Student findStudentWithName(List<Student> students, String name) {
    for (Student s : students) {
        if (s.getName().equalsIgnoreCase(name)) {
            return s;
        }
    }
    // no student found.
    return null;
}