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2 Answer(s)      6 years and 6 months ago
Posted in : Java Beginners

what is NullPointerException?

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October 18, 2010 at 9:17 PM


Hi,

I java NullPointerException java.lang.NullPointerException) is defined in the java.lang package.

The NullPointerException is thrown by the Java program at the time of execution of the application.

Following are the regions of NullPointerException in Java program:

* If you are calling some method on the null object.
* Modifying or accessing the field of a null object.
* Trying to get the length of null as if it were an array.
* Throwing null value.

In the following code if you try to call the length method the Java program will though NullPointerException:

class HelloWorld 
{
    public static void main(String[] args) 
    {
        System.out.println("Hello World!");
        String s=null;
        int iLenght = s.length();
        System.out.println("Length is: " + iLength);
    }
}

Thanks



October 18, 2010 at 9:24 PM


Hi,

Here are the tips to avoid NullPointerException in Java program:

a) Define the variable and initialize it with some value: e.g:

   String s="Some Value";
   int i = 100;

etc.

b) Avoid performing the add/divide/minus etc. operations on null objects.

c) If you are not sure that a variable is null or not then check it before use: e.g.

   if (counter != null) {   
     counter=counter+step;
   }

Thanks










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