How CheckNotNull works

[Ashwin Bharadwaj]

Hi ,

Can anyone please explain me how exactly CheckNotNull works.

Thanks,
Ashwin

[Mohamed Sanaulla]

Ashwin ks wrote:Hi ,

Can anyone please explain me how exactly CheckNotNull works.

Thanks,
Ashwin

Hi Ashwin, Welcome to Java Ranch!
Can you give more context to this? I dont think "CheckNotNull" is from the Java API.

[Ashwin Bharadwaj]

Hi Mohammed,

I m new to java ... i came across a scenario where in the code in if condition check NotNull is used so i want to know how exactly it works.

Thanks for your response Mohammed

Thanks,
Ashwin

[Mohamed Sanaulla]

Ashwin ks wrote:Hi Mohammed,

I m new to java ... i came across a scenario where in the code in if condition check NotNull is used so i want to know how exactly it works.

Can you tell us the reference where you found this usage? Or better post a simple working code. It will help us to clear your doubt easily.

[Ashwin Bharadwaj]

if ((user.equals("customer"))) {
selectRadioButton(USERCUSTOMERRADIO);
enterText(USERCUSTOMERTEXTBOX, name);
} else {
selectRadioButton(USERSUPPLIERRADIO);
enterText(USERSUPPLIERTEXTBOX, name);
}
clickElement(CHANGEBUTTON, DEFAULTWAIT);
}


I want know how use not null in these case.

[Mohamed Sanaulla]

Ashwin ks wrote:

if ((user.equals("customer"))) {
            selectRadioButton(USERCUSTOMERRADIO);
            enterText(USERCUSTOMERTEXTBOX, name);
        } else {
            selectRadioButton(USERSUPPLIERRADIO);
            enterText(USERSUPPLIERTEXTBOX, name);
        }
        clickElement(CHANGEBUTTON, DEFAULTWAIT);
    }
              

I want know how use not null in these case.

Please use the [code]tags to post your code.

Am not able to see your Use case here- You want to check if the value is not null? Then you could use- <variable> != null, or to check for empty string you could try- <variable>.equals("").

[Ashwin Bharadwaj]

OK thanks a lot

[Jan Hoppmann]

mohammed sanaullah wrote:Am not able to see your Use case here- You want to check if the value is not null? Then you could use- <variable> != null, or to check for empty string you could try- <variable>.equals("").

But remember that an empty String ("") is not the same as null.

[fred rosenberger]

Jan Hoppmann wrote:But remember that an empty String ("") is not the same as null.

This sometimes confuses people. A good way to think of the difference is an empty string is a box with nothing in it. A null string means you don't even have a box.

[Mohamed Sanaulla]

fred rosenberger wrote:
This sometimes confuses people. A good way to think of the difference is an empty string is a box with nothing in it. A null string means you don't even have a box.

Nice example!

[Campbell Ritchie]

Why are you using such a test in a Listener? That sounds to me like very non-object-oriented programming. You have probably got some poor design there. You can avoid problems with null Strings very easily, by swapping the order of operands, like this:

if ("customer".equals(user)) . . .

That test cannot suffer a NullPointerException even if user is null.

There are a few instances where a formal null check is required: for example in the old-fashioned use of a FileReader. Note I am showing the correct way to do it with a finally block. Look at this post, and the post farther down where I realised I had made a mistake. That will show you how to check for nullity.

[Ashwin Bharadwaj]

Thanks to all for the response.

[Campbell Ritchie]

You're welcome