JAVA: Null Pointer Exception error

Question

Hello All I'm writing some code and keep getting a Null Pointer Exception and for some reason I'm just hitting a mental wall.

Now I do know that null pointer is when the value its trying to use is null, but I can't seem to figure out how to fix the problem. (Errored Line is *'d out.)

   public static void getMenuChoice(Dog s) {
      int LCV = 0;
     Scanner in = null; // create a scanner object
  do {
     System.out.println("Welcome to the Input Menu");
     System.out.println("1: Assign the name");
     System.out.println("2: Assign the owner");
     System.out.println("3: Assign the age");
     System.out.println("4: Assign the weight");
     System.out.println("5: Assign the breed");
     System.out.println("6: Assign the time");
     System.out.println("7: Display Dog Information");
     System.out.println("8: Quit");
     System.out.print("Choose a Menu Option => ");


     ****************int input = in.nextInt();*********************

     switch (input) {
        case 1:
           System.out.println("Please Enter the Dogs name");
           s.setDogName(in.next());
           break;
        case 2:
           System.out.println("Please Enter the Owners name");
           s.setOwnerName(in.next());
           break;
        case 3:
           System.out.println("Please Enter the Dogs age");
           s.setDogAge(in.nextDouble());
           break;
        case 4:
           System.out.println("Please Enter the Dogs weight");
           s.setWeight(in.nextDouble());
           break;
        case 5:
           System.out.println("Please Enter the Dogs breed");
           s.setDogName(in.next());
           break;
        case 6:
           System.out.println("Please Enter the Time");
           s.setTime(in.nextDouble());
           break;
        case 7:
           System.out.println(s);
           break;
        case 8:
           LCV = 8;
           break;
     }
  } while (LCV != 8);

}

Well, you don't initialize your `Scanner`... Except to `null` — fge, Apr 09 '15 at 14:32
c++ was a suggested tag. As a very new member to the community, I tend to go with the suggest tags. — SynGaren NA, Apr 09 '15 at 14:42

score 2 · Accepted Answer · edited Jun 20 '20 at 09:12

Your Scanner not initialized ,you shoud do

Scanner in = new Scanner(System.in);  // instead of  Scanner in = null;

So when you are doing

in.nextInt();   // null.nextInt()

you are getting NullPointerException

public class NullPointerException extends RuntimeException

Thrown when an application attempts to use null in a case where an object is required. These include:

Calling the instance method of a null object.

Accessing or modifying the field of a null object.

Taking the length of null as if it were an array.

Accessing or modifying the slots of null as if it were an array.

Throwing null as if it were a Throwable value.

Docs

score 1 · Answer 2 · answered Apr 09 '15 at 14:32

A NullPointerException means you are dereferencing a variable which has not been instantiated (a variable which points to null). Here's your declaration of in:

Scanner in = null;

You have a null variable here, which you then dereference:

int input = in.nextInt();

This causes your NullPointerException. You need to instantiate in somehow like

Scanner in = new Scanner(System.in);

JAVA: Null Pointer Exception error

2 Answers2