Problem with constructing an ArrayList

[Diplo]

Hi all. I'm in my first year at university doing computer science and having a little trouble with an assigment. I'm trying to construct an ArrayList containing a number of Students which are in a College. (Students and College are both classes) However, the ArrayList<Student> seems to come up null, meaning the students aren't being added.

Obviously there is more code and I will post if requested but I think I'm just making a fairly basic error. Thanks in advance for any help.

import java.util.Random;
import java.util.ArrayList;

public class College
{
        
    private ArrayList<Student> sArr;
    private Library aLibrary;
    private Random random;
    
    public College(int nStudents, int nBooks)
    {
        aLibrary = new Library(nBooks);
        ArrayList<Student> sArr = new ArrayList<Student>(nStudents);
        for (int j = 0; j < nStudents; j++) {
            String name = "Student" + j;
            Student newStudent = new Student(name, aLibrary);
            sArr.add(newStudent);
        }

[RamyaSivakanth]

check whether newStudent is null by putting s.o.p

[JosAH]

import java.util.Random;
import java.util.ArrayList;

public class College
{
        
    private ArrayList<Student> sArr;
    private Library aLibrary;
    private Random random;
    
    public College(int nStudents, int nBooks)
    {
        aLibrary = new Library(nBooks);
        ArrayList<Student> sArr = new ArrayList<Student>(nStudents);
        for (int j = 0; j < nStudents; j++) {
            String name = "Student" + j;
            Student newStudent = new Student(name, aLibrary);
            sArr.add(newStudent);
        }

You have two sArr variables: one is a member variable and it is null (by definition); the other one is a local variable, local to your constructor. You obviously don't want that so you should change that line to:

        sArr = new ArrayList<Student>(nStudents);

kind regards,

Jos

[Diplo]

Many thanks Jos that worked perfectly.

As a matter of interest, what is an s.o.p?

[RamyaSivakanth]

Hi Jos,
Even I missed the arraylist initialized part....Great!!!!!!!1

[JosAH]

As a matter of interest, what is an s.o.p?

Some people who are too lazy to type use s.o.p. for System.out.println( ... )

kind regards,

Jos