Null Pointer Exception in Array List- How do objects work?

Question

I am having null pointer exception. Could you please assist me? I am having problems with objects in the Array list. I don't know where is the issue.

Main Class

public class JavaApplication3 {

 public static void main(String[] args) {


     ArrayList<user> object=new ArrayList<user>();

   user[] obj=new user[3];

    obj[0].setName("S");

    obj[0].setNumber(5);

      obj[1].setName("7");

    obj[1].setNumber(6);
     object.add(obj[0]);

       object.add(obj[1]);
    System.out.println(object.get(0).getName());
    System.out.println(object.get(1).getName());





 }

}

And this is my user class:

public class user {

 private int no;
 private String name;

   public int getNo() {
     return this.no;
 }

 public void setNumber(int no) {
     this.no = no;
 }


 public String getName(){

 return this.name;
 }

 public void setName(String S){

     this.name=name;

 }

}

AND THIS IS MY ERROR:

Picked up _JAVA_OPTIONS: -Djava.net.preferIPv4Stack=true
Exception in thread "main" java.lang.NullPointerException
    at javaapplication3.JavaApplication3.main(JavaApplication3.java:26)
C:\Users\User\AppData\Local\NetBeans\Cache\12.3\executor-snippets\run.xml:111: The following error occurred while executing this line:
C:\Users\User\AppData\Local\NetBeans\Cache\12.3\executor-snippets\run.xml:68: Java returned: 1
BUILD FAILED (total time: 0 seconds)

You need to instantiate each User before you can set any property. — aksappy, Apr 20 '21 at 18:48
You created an array of users user[] obj=new user[3];, but you forgot to create a user for each position, like user[0] = new User(); — dreamcrash, Apr 20 '21 at 18:48
Can you help me fix the code? I tied user[0]=new user(); but still not working. — LEARNWITHPASSION, Apr 20 '21 at 18:52

Abdalrhman Alkraien · Accepted Answer · 2021-04-20T19:11:57.610

0

just convert this from S to name

 public void setName(String name){
    
        this.name=name;
    
    }

and change to this code

ArrayList<user> object=new ArrayList<user>();
 user[] obj=new user[3]; 
obj[0]=new user(); 
obj[2]=new user(); 
obj[0].setName("S"); 
obj[0].setNumber(5);
 obj[1]=new user(); 
obj[1].setName("7");
 obj[1].setNumber(6); 
object.add(obj[0]); 
object.add(obj[1]);
 System.out.println(object.get(0).getName()); System.out.println(object.get(1).getName());

edited Apr 20 '21 at 19:11

answered Apr 20 '21 at 19:03

Abdalrhman Alkraien

107
8

Already done that but the problem is still there- – LEARNWITHPASSION Apr 20 '21 at 19:05
ArrayList object=new ArrayList(); user[] obj=new user[3]; obj[0]=new user(); obj[2]=new user(); obj[0].setName("S"); obj[0].setNumber(5); obj[1]=new user(); obj[1].setName("7"); obj[1].setNumber(6); object.add(obj[0]); object.add(obj[1]); System.out.println(object.get(0).getName()); System.out.println(object.get(1).getName()); – Abdalrhman Alkraien Apr 20 '21 at 19:09
this is solved your problem – Abdalrhman Alkraien Apr 20 '21 at 19:09
you must add in your code obj[0]=new user(); and obj [1]=new user(); – Abdalrhman Alkraien Apr 20 '21 at 19:10

Null Pointer Exception in Array List- How do objects work?

1 Answers1