String ArrayList returning null values

Question

I am new to java and doing some arraylist work, and when compiling my lists just return null values instead of names I have typed in.

I don't understand why this is so, so if anyone could advise/help me that would be great.

Here is my main code

import java.util.*;

public class StudentData 
{
    public static void main(String[] args) 
    {
        Scanner in = new Scanner(System.in);
        ArrayList<Student> studentList = new ArrayList<Student>();
        String yesNo = "true";
        do
        {
            System.out.println("Enter student's name: ");
            String name = in.next();
            Student s = new Student();   
            studentList.add(s);
            String input;
            do
            {   
                System.out.println("Would you like to enter data for another student? Yes/No ");
                yesNo = in.next();
                }
            while (!yesNo.equalsIgnoreCase("YES") && !yesNo.equalsIgnoreCase("NO"));
            }   
        while (yesNo.equalsIgnoreCase("YES"));
            
        
        for(int i = 0; i < studentList.size(); i++)
        {
            System.out.println(studentList.get(i).getName());
            }
        }
    }

And

class Student 
{
    private String studentName;
    
    public StudentData(String name)
    {
        setName(name);
    }
    public String getName()
    {
        return studentName;
        }
    public void setName(String name)
    {
        studentName = name;
        }
    }

Because student names are not initialised. This is reason why your values are null. — Simon Dorociak
– Simon Dorociak, Commented Dec 2, 2013 at 22:41
This shouldn't compile...You defined your class as Student but have a constructor defined as public StudentData(String name)... — MadProgrammer
– MadProgrammer, Commented Dec 2, 2013 at 22:43

user2336315 · Accepted Answer · 2013-12-02 22:40:33Z

4

You're creating a student but didn't set the name :

            String name = in.next();
            Student s = new Student();   
            studentList.add(s);

Try with :

        String name = in.next();
        Student s = new Student();   
        s.setName(name);
        studentList.add(s);

Also replace your constructor. I.e :

public StudentData(String name){
        setName(name);
}

should be

public Student(String name) {
        setName(name);
}

Then you will be able to do Student s = new Student(name);

answered Dec 2, 2013 at 22:40

user2336315

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