Nullpointer exception fixed problem

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How do i fix NullPointerException? cant fixed the problem

NullPointerException is thrown when a reference variable is accessed (or de-referenced) and is not pointing to any object. This error can be resolved by using a try-catch block or an if-else condition to check if a reference variable is null before dereferencing it.

a special null value can be assigned to an object reference. NullPointerException is thrown when program attempts to use an object reference that has the null value.

What I have tried:

cant fixed

This error can be resolved by using a try-catch block or an if-else condition to check if a reference variable is null before dereferencing it.

Posted 6-Dec-21 14:48pm

Sesaria Titis

Updated 6-Dec-21 20:31pm

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Stefan_Lang 7-Dec-21 3:21am

Please do not tag your post as C++ when you're not talking about C++. Judging by your description, this can't be C++.

Also, when you ask for help, remember that we cannot see your monitor, and that we cannot read your mind. You have not told us what you want, only what you get. And you haven't shown us any code, so we have no basis to help you, beyond an abstract description of the steps you should take to help yourself (see solution 1)

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OriginalGriff · Answer 1 · 2021-12-06T19:24:00

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterday's shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, it will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, the debugger will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

KarstenK · Answer 2 · 2021-12-06T20:31:00

Solution 2

The normal way is to check before using the var like

C++

if( myPointer != 0 ) {
  myPointer->executeMyTask();
  return true;
} else {
  // some error handling: here existing the code path
  return false;
}

Posted 6-Dec-21 20:31pm

KarstenK

Comments

Stefan_Lang 7-Dec-21 3:13am

The post is tagged as both C++ and Java, but the OP talks about assigning a null reference - this indicates it's Java, not C++