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Thread: ArrayLists and Classes

  1. #1
    Member melki0795's Avatar
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    Unhappy ArrayLists and Classes

    Hi, I have this piece of code, which adds marks into 2 different arrayLists, one for homework marks, and one for examination marks..


     
    ArrayList<Double> homeworkMark = new ArrayList<Double>();
    ArrayList<Double> examinationMark = new ArrayList<Double>();
     
    boolean markCheck = true;
            do{
           //the purpose of this try catch is to make sure that the entered mark is a valid number. If the program encounters an exception markCheck will become true and the loop will begin again asking the user to enter the marks. If the marks are all encountered correctly markCheck will be false and the loop will end.
            try{
             for (int i = 1; i <= amountAssignment; i++ ) {
               sc.reset();
               System.out.print("Homework Mark for Assignment " +(i) + ": ");
               homeworkMark.add(sc.nextDouble());
               System.out.print("Examination Mark for Assignment " + (i) + ": ");
               examinationMark.add(sc.nextDouble());
               markCheck = false;
     
             }
           }catch (Exception e) {
             e.printStackTrace();
             System.out.println("------------");
             System.out.println("|  ERROR   |");
             System.out.println("------------");
             System.out.println("You'll have to enter your marks again!") ;
             System.out.println("");
             markCheck = true;
     
           }
          }while (markCheck == true);


    I need to add the data from this arrayList in the Main method into an arrayList in a different class, named subject, which can found below...

     
    import java.util.ArrayList;
    public class subject
    {
       int subjectNumber;
     
     
        public subject(int subjectNumber) {
          this.subjectNumber = subjectNumber;  
     
       }
     
       public int getSubjectNumber() {
           return subjectNumber; 
        }
     
       void setSubjectNumber (int subNum) {
            subjectNumber= subNum;
       }
     
    }

    I have no idea how to do this and I've tried multiple things but cannot seem to get anywhere... :-(

    Regards


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: ArrayLists and Classes

    One way to get data from another class is to add a getter method in the class with the data and use that in the method in another class to access the data in the class with the data.

    arrayList in the Main method
    If the arraylists are defined inside of a method, a getter method will not be able to access it. The arraylist needs to be defined as an instance member of the class.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: ArrayLists and Classes

    I don't disagree with anything Norm said, but you said, "I need to add the data from this arrayList in the Main method into an arrayList in a different class," which is slightly different. You could create a method in the other class, Subject, called (for example), addListItems( ArrayList items ), that adds the argument ArrayList's members to the ArrayList in an instance of Subject. Then in main(), you would do something like:

    Subject subject = new Subject();

    subject.addListItems( mainArrayList );

    where mainArrayList is the ArrayList in main() that you want to add to the other class' ArrayList.

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    Default Re: ArrayLists and Classes

    You've continued this topic in another thread. I'm not merging them, because I think it would be confusing, so I'll just close this one.

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