How can I return ArrayList values from a Class in Java

Question

Here's my code: The code should return the list of students with the relevant data from the arraylist. But the error is telling me it can't make a static reference to a non static method??

I've tried to make the methods static and it gives me another error.

//main function code
    String forename = null;
    String surname = null;
    String grade = null;
    String yesOrNo;
    double mark;
    int selection;

ArrayList<StudentClass> studentDetails = new ArrayList<StudentClass>();

switch(selection){
case 1: {
    if (studentDetails.isEmpty()){
        System.out.println("No Students Have Been Entered Yet");
        main(null);
        break;
                }
    else{
         for(int i = 0; i < studentDetails.size(); i++){
             StudentClass = studentDetails.get(i);
             System.out.println( StudentClass.getForename() + " " +
             StudentClass.getSurname() + " received a " + StudentClass.getGrade() +
             " for their Student Mark of " + StudentClass.getMark() + "." );
            }
        }
break;
\\ Error:Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
StudentClass cannot be resolved to a variable
Cannot make a static reference to the non-static method getForename() from the   type StudentClass
Cannot make a static reference to the non-static method getSurname() from the type StudentClass
Cannot make a static reference to the non-static method getGrade() from the type StudentClass
Cannot make a static reference to the non-static method getMark() from the type StudentClass

at students.main(students.java:60)
\\code for Class
public class  StudentClass {
      public String Forename;
      public String Surname;
      public  String Grade;
       public  double Mark;

public StudentClass(String forename, String surname, double mark){

       Forename = forename;
   Surname = surname;
   Mark = mark;
   }

  public void setForename(String forename)
    {
        Forename= forename;
    }

  public void setSurname(String surname)
    {
        Surname= surname;
    }

  public void setMark(double mark)
    {
        Mark= mark;
    }

  public  String getForename()
    {
        return Forename;
    }

  public  String getSurname()
    {
        return Surname;
    }

  public  double getMark()
    {
        return Mark;
    }
  public  String getGrade()
    {   
            if ( Mark < 40 )
                Grade = "FAIL";
            else if ( (Mark >= 40) && (Mark <= 64) )
                Grade ="PASS";
            else if ( (Mark >= 65) && (Mark <= 84) )
                Grade ="MERIT";
            else if ( (Mark >= 85) && (Mark <= 100) )
                Grade ="DISTINCTION";
            return Grade;
}
  }

John3136 · Accepted Answer · 2013-10-23 05:22:37Z

1

StudentClass = studentDetails.get(i); makes no sense. StudentClass is a classname.

You need an instance: StudentClass student = studentDetails.get(i); Then use student.getSurname() etc.

answered Oct 23, 2013 at 5:22

John3136

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Comments

sandymatt · Accepted Answer · 2013-10-23 05:21:56Z

0

StudentClass.getSurname() is not defined as a static method. You need to declare an instance of that class in order to be able to call it.

StudentClass myClass = new StudentClass(/* whatever params you need*/);
String surname = myClass.getSurname();

keep in mind you need to do this for all those methods, as they're at the instance level.

answered Oct 23, 2013 at 5:21

sandymatt

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Comments

Terry Li · Accepted Answer · 2013-10-23 05:23:16Z

for(int i = 0; i < studentDetails.size(); i++){
             StudentClass = studentDetails.get(i);
             System.out.println( StudentClass.getForename() + " " +
             StudentClass.getSurname() + " received a " + StudentClass.getGrade() +
             " for their Student Mark of " + StudentClass.getMark() + "." );
            }

Change the code above to:

    for(int i = 0; i < studentDetails.size(); i++){
        StudentClass student = studentDetails.get(i);
        System.out.println( student.getForename() + " " +
        student.getSurname() + " received a " + student.getGrade() +
                 " for their Student Mark of " + student.getMark() + "." );
   }

See if the error will be gone. The compiler was complaining because you were trying to invoke an instance level (non-static) method on the class itself (rather than an instance of the class).

Rajaprabhu Aravindasamy · Accepted Answer · 2013-10-23 05:25:14Z

0

Non-static method in java cannot be accessed with out an object

Just try like this,

else{
         for(int i = 0; i < studentDetails.size(); i++){
             studentDetails.get(i) = new StudentClass();
             System.out.println( studentDetails.get(i).getForename() + " " +
             studentDetails.get(i).getSurname() + " received a " + studentDetails.get(i).getGrade() +
             " for their Student Mark of " + studentDetails.get(i).getMark() + "." );
            }
        }

answered Oct 23, 2013 at 5:25

Rajaprabhu Aravindasamy

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