Exception in thread "main" java.lang.NullPointerException

[deepika deepi]

hi all,

Good morning. I am developing an program to call integer from one method to another. in this i am getting the output window. but getting an exception.
Error:

Exception in thread "main" java.lang.NullPointerException

if i type yes or Yes. How to solve this. ??

here is the code

public class Foo {


//public static final Integer intMoney = 500;
public static Integer intMoney;

    //public static void program1(String[] args) { changed to
public static void program1() {
        intMoney = 500;
    }

    public static void main(String[] args) {
        String strYes;
        strYes = JOptionPane.showInputDialog("type yes to subtract 100");
        if ((strYes.equals("Yes") || (strYes.equals("yes"))))
        {
            Integer i = intMoney;
            Integer x = i - 100;

        }else{
            JOptionPane.showMessageDialog(null, "Thats not yes!");

        }
    }
}

[Divya Janyavula]

Post the exact location of your exception in the code or post the complete stack trace. Also check if your strYes variable has null value.

Also you have not called the program1 method and intMoney variable value will be null. This also might be the problem

[deepika deepi]

ya solved. thank you.

[Ankush Kaundal]

The exception is coming because your variable intMoney is not initialized as you have not called the static method program1() so solution is to either call this method or put the code on line 09 in static block rather than in method.

[Campbell Ritchie]

Design error. Every field ought to be initialised to establish the class invariant in the constructor.

[deepika deepi]

ya. i changed the code it's not giving any error now.

[shaileshkumar mistry]

Hi Deepika

As you can see that Integer is a wrapper class so the default value when class initialized your intMoney will be null,

and when you do Integer i =intMoney the i also will reference to a null object.

so when you do an Integer x=i-10 the value of i is null , the wrapper object's can not convert null to 0 or vice versa so it will give null pointer exception.