Thread: NullPointerException but dont know why

When I run class Programmalijst, I get a NullpointerException.
It states that my x.hasNext() is null, I dont know why. Im a beginner in Java.

import java.util.*;
import java.io.File;
 
 
public class Datatype {
 
	public Scanner x;
 
	public void openFile (){
		try{
			x = new Scanner (new File("programmas.txt"));
 
		}
		catch(Exception e){
			System.out.println("error could not find file");
		}
	}
 
	public void getZender(){
		while(x.hasNext()) {
			String zender = x.next();
			System.out.println(zender);
		}
 
	}
public void closeFile (){
		x.close(); 
	}
 
}

public class Programmalijst {
 
	public static void main (String [] args){
 
		Datatype r = new Datatype ();
 
		r.getZender();
}
}

Welcome to the forum! Thanks for taking the time to learn how to post code correctly. If you haven't already, please read this topic to learn other useful info for new members.

Posting the entire error message and stack trace is helpful, because it includes important information.

The variable 'x' is initialized inside the method openFile(). If that is not done before the method getZender() is called, it will be null or uninitialized when called in getZender(). The solution is to ensure it has been initialized using a 'new' statement before it is used anywhere in the program. Those kind of initializations are often done in a constructor but can be done anywhere as long as it gets done.

Thank you, however I put r.openFile() in it, but I still get the same exception.

Those kind of errors are sometimes can be hard to handle so it's important for you to try and detect them as quick as possible.
If it's getting too hard for you, you can try using some programs, such as checkmarx or others to help you do that.
Good luck!
Ben.

NullPointerExceptions are exceptions that occur when you try to use a reference that points to no location in memory (null) as though it were referencing an object. Calling a method on a null reference or trying to access a field of a null reference will trigger a NullPointerException. These are the most common, but other ways are listed on the NullPointerException javadoc page.

Probably the quickest example code I could come up with to illustrate a NullPointerException would be:

public class Example {

public static void main(String[] args) {
Object obj = null;
obj.hashCode();
}

}