java.lang.NullPointerException even though it's instanciated as global var

Question

my problem is easy normally but i just don't see where is the problem. -i am declaring an array of a class as a global variable that i reuse in multiple functions inside this other class. the class instantiated is:

 public class Service {
      int numticketsin;
            String name="mi";
            int[] perhour={0,0,0,0,0,0,0,0,0,0};
            
            int moyenneticketperday;
            int[] moyenneticketperdayperhour={0,0,0,0,0,0,0,0,0,0};
            public Service(){}
}

global var:

Service[] services=new Service[10];

the function where i use try to fill the array:

 public void getnamesofservices(){
        int x=0;
        Connection conn=db.java_db();
    
        try {   
             Statement stmt = conn.createStatement();
            
                String qry = "SELECT  service_name from service ";
 
                ResultSet rs = stmt.executeQuery(qry);
                int i=0;
                while (rs.next()) {
                        String namee=rs.getString("service_name");
                        System.out.println(namee);

                        services[i].name = namee;
                   i++;
                }
                conn.close();
                
        }
        catch (SQLException ex)
            {
            System.err.println("SQLException: " + ex);
        }
        
    }

the error:

''' Exception in thread "main" java.lang.NullPointerException: Cannot assign field "name" because "this.services[i]" is null
    at com.mycompany.stats.NewJFrame.getnamesofservices(NewJFrame.java:195)
    at com.mycompany.stats.NewJFrame.<init>(NewJFrame.java:122)
    at com.mycompany.stats.Main.main(Main.java:16)'''

thank you in advance!!

So which line is line 195? (I'd also strongly advise that you start following Java naming conventions, e.g. `getNamesOfServices` - or just `getServiceNames` instead of `getnamesofservices`, as well as a better name than `java_db`. — Jon Skeet, Dec 27 '21 at 10:04
`new Service[10]` means you _allocate_ a 10 elements array of `Service` instances that are initially `null`, but it does not mean you initialize each element, therefore all of the elements are `null` after the allocation. Seriously, why not debug it first and initialize the array properly? — terrorrussia-keeps-killing, Dec 27 '21 at 10:05
[NullPointerException when Creating an Array of objects](https://stackoverflow.com/questions/1922677/nullpointerexception-when-creating-an-array-of-objects) — OH GOD SPIDERS, Dec 27 '21 at 10:19

gmanjon · Accepted Answer · 2021-12-27T10:10:18.137

Service[] services=new Service[10];

This means you created and array with 10 positions, but all those positions are empty (meaning they have null inside each and every position of the array).

So, when trying services[i].name you get the NullPointerException because services[i] is null.

There are plenty of ways to do the initialization, that depends on your business cases. But just to name two possibilities:

Initialize it at the declaration:

Service services[] = new Service[] { 
   new Service(),new Service(), new Service(), new Service(),new Service(),
   new Service(),new Service(), new Service(), new Service(),new Service()
};

Or just before using it, in case you are not overriding it:

services[i] = new Service();
services[i].name = namee;

java.lang.NullPointerException even though it's instanciated as global var

1 Answers1