How to search for an element in an ArrayList using a string?

Question

I am writing a program to keep track a school's classes and students. I have School, Classroom, and Student objects. The school contains an ArrayList of classroom objects and each classroom contains an ArrayList of student objects.

I am trying to write a method in the School class to remove a student using a String name and String classroomName as a parameter.

This is what I have so far:

public void remove( String studentName, String classroomName) {
    for(Classroom c : classes) {
        if(c.className.equals(classroomName)){
         //search for student and remove
          for(Student s : students){
             if(s.studentName.equals(studentName)){
                s.remove(studentName);
        }
      }
    }
}

I think this is not working because the ArrayList of Student objects is declared in the Classroom class.

Is there a way to search through an object ArrayList for an element using a non object parameter?

You cannot remove element of a list while iterating on it (except if you explicitly use an iterator). See: stackoverflow.com/questions/49668278/… — Arnaud Denoyelle
– Arnaud Denoyelle, Commented Sep 18, 2018 at 15:37
Can you do c.students in nested loop? Also, don;t concurrently alter a collection while you are iterating over it. — nabster
– nabster, Commented Sep 18, 2018 at 15:37
Possible duplicate of : stackoverflow.com/questions/10431981/… — dbl
– dbl, Commented Sep 18, 2018 at 15:38
Apart from that, you don't want to replace studentName from student (in the inner for loop). You actually want to replace s from students. — Arnaud Denoyelle
– Arnaud Denoyelle, Commented Sep 18, 2018 at 15:39

samugi · Accepted Answer · 2018-09-18 15:50:07Z

1

Like they told you, you can't remove an element from a list while iterating on it unless you use an iterator or you manually control the iteration with indexes.

Otherwise, if you're using Java 8 you can go with:

students.removeIf(s -> s.studentName.equals(studentName));

answered Sep 18, 2018 at 15:50

samugi

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1 Comment

Doctor Parameter Over a year ago

you would need to do a filter on classes to get the students.

RaffleBuffle · Accepted Answer · 2018-09-18 16:17:39Z

0

As others have noted, you can only remove elements with an Iterator. You want something like this:

    for(Iterator<Student> it = c.students.iterator(); it.hasNext();)
    {
        Student s = it.next();
        if(s.studentName.equals(studentName))
            it.remove();
    }

You say that each Classroom contains a List of Students, so I'm assuming c.students is what you want to iterate over - your posted code uses a standalone list students. Maybe that's a typo?

answered Sep 18, 2018 at 16:17

RaffleBuffle

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