CODEWITHSUNDEEP
java
Satya
Satya

Reputation: 8881

NullPointerException when accessing static variable in another class in Java

I have trying to access a static variable of class A in class B, however I am getting NullPointerException. The code is :

public class OutgoingMessage {
    public static SMPPSession session;
    public static void main(String [] args)
    {
         session = new SMPPSession();

    }
  }

And 

public class SendSMS {
    public static void main(String [] args)
    {
      if(OutgoingMessage.session.getSessionState().toString().equals("Connected"))//Line 44 
        {
        }
    } 
}

The error reads 

Exception in thread "main" java.lang.NullPointerException
        at SendSMS.main(SendSMS.java:44)

Any idea what am I missing ?

Thanks

Satya

Upvotes: 0

Views: 2923

Answers (6)

Jafar Mirzaei
Jafar Mirzaei

Reputation: 57

You can add OutgoingMessage.main(args); before:

if(OutgoingMessage.session.getSessionState().toString().equals("Connected")) //Line 44 ...

Upvotes: 1

Rohit Jain
Rohit Jain

Reputation: 213263

You haven't initialized your static variable.. That's why..

Actually you have done that in main(), but that will really not affect your output.. As your main will never be run.. You can initialize it at the place of declaration only..

public static SMPPSession session = new SMPPSession();

Before main method.. But it doesn't make sense to have it as static variable..

You should declare it as instance variable and initialize it for each instance you create using a Constructor..

Upvotes: 0

Filipe Borges
Filipe Borges

Reputation: 2793

The problem is when you use OutgoingMessage.session it is not yet initialized. To correctly initialize it do:

public class OutgoingMessage {
    public static SMPPSession session = new SMPPSession();
  }

Upvotes: 0

Jordan Denison
Jordan Denison

Reputation: 2727

You are missing a static getter method in OutgoingMessage, and you only need one main method.

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1500665

Sure - you're using OutgoingMessage.session, which will be null unless you've also run OutgoingMessage.main. It's not like main methods get invoked automatically everywhere - that's just the entry point for the application.

I suggest that instead of changing this to use a static initializer or something like that, you try to work to avoid static variables.

Why would it make sense for OutgoingMessage to have a static session variable? I'd expect the two to work together, not one be composed of the other... for example, I could imagine:

SMPPSession session = new SMPPSession();
session.send(outgoingMessage);

or even:

SMPPSession session = new SMPPSession();
outgoingMessage.sendInSession(session);

Upvotes: 6

kosa
kosa

Reputation: 66637

OutgoingMessage.session is null at the point where you are calling 

if(OutgoingMessage.session.getSessionState()

Which results in NullPointerException.

Make sure OutgoingMessage class main method is executed before making if(OutgoingMessage.session.getSessionState()

Unless you use OutgoingMessage as main class, it doesn't make sense to define main method there, which confuses more.

Upvotes: 2

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