Initializing an array of class type variables.

[xpl0rerchr]

So, this is the Student class and its constructor.

public class Student {
    
    public enum Status {ACTIVE, INACTIVE};
    
    private String name;
    private int aem;
    private int year;
    private Status status = Status.ACTIVE;
    Course[] coursesReg;
    private int numCoursesReg = 0;
    private final int MAX_COURSES = 54;  
    
    
    Student(String name, int aem, int year) {
        this.name = name;
        this.aem = aem;
        this.year = year;
    }
}

And this is the UniClass class, its constructor and its addStudent function.

public class UniClass {
    
    private int classYear;
    private int initId;
    Student[] students;       // This is the array of Student objects I'm having problems with.
    private int numStudents;
    private final int MAX_STUDENTS = 150;
    
    UniClass(int year, int aem) {
        classYear = year;
        initId = aem;
        numStudents = 0;
    }

    boolean addStudent(String name) {
        int aem = initId;
        if (students.length == MAX_STUDENTS) {
            return false;
        }
        for (int i = 0; i < MAX_STUDENTS; i++) {
            if (students[i] == null) { 
                students[i] = new Student(name, aem, classYear);    // This is where I'm getting the NullPointerException.
                initId++;
                numStudents++;
                return true;
            }
        }
        return false;
    }
}

Now, as I'm trying to add a new student in addStudent, I'm getting a NullPointerException. Why would this be? I've already created an instance of UniClass.
And I had previously (now I've deleted that part) tried to set each cell in the "students" array to null, and I was also getting the NullPointerException thing. Should I be initializing that array somehow differently than I tried, or is something else wrong?
PS. I'm a begginer at Java, if that's not obvious already. I have a lot of experience with C, though.

Your help is much appreciated!

[KevinWorkman]

When do you initialize the students array?

Recommended reading: http://docs.oracle.com/javase/tutori...ts/arrays.html

[xpl0rerchr]

When do you initialize the students array?

Recommended reading: Arrays (The Java™ Tutorials > Learning the Java Language > Language Basics)

As I said, "(...) I had previously (now I've deleted that part) tried to set each cell in the "students" array to null, and I was also getting the NullPointerException thing. Should I be initializing that array somehow differently than I tried, or is something else wrong?".

ΕDIT: You were right, I hadn't initialized it the way arrays are supposed to be initialized. I guess I'm still too used to the for loop used in C for this purpose.

[Tolls]

No, Kevin means when do you initialise this:

Student[] students;

This simply declares a variable, but 'students' is not pointing at anything...it is null.

[xpl0rerchr]

No, Kevin means when do you initialise this:

Student[] students;

This simply declares a variable, but 'students' is not pointing at anything...it is null.

You are right, I realised just a while ago what he really meant. Thank you for clarifying this.
I did the following:

Student[] students = new Student[MAX_STUDENTS];

[DarrylBurke]

Moved from NetBeans.

db