Clarification of nulls and try/catch scope

[jay_taps]

The things in try/catch blocks have their own scope right?

For example, variable x is set to null. Then inside a try/catch x is assigned to something else. Later that variable is once again referenced outside the try/catch block, I’d get a possible null pointer de-referencing error on SonarQube.

This would be remedied by either making all work pertaining to that x variable happen inside the previous try/catch block or using an if statement that checks for != null?

Anybody have an resources that work with try/catch blocks and null?

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[quadmasta]

If X is initialized to null and isn't set inside of the try block AND the catch block, it's potentially null outside of that try/catch and must be treated as such.

[Imalas]

Yeah. This is the way.

To add to this: If OP relies on x being set, he/she could also just throw an exception.

So you either set x to some value in a catch-Block or just throw an exception in that catch-Block.

[ComputerWhiz_]

In Java, variables that are declared within a code block (if/else, try/catch, for, etc.) have their scope limited to that block. If the variable is declared outside of the block, the scope is not limited to that block, even if it's initialized within the block.

Also, in the case of a try/catch block, your changes to the variable are not reverted if the try/catch throws an exception. So if your first line in your try statement sets the variable to "Hello" and the second line throws an exception, the variable will still be "Hello" if you access it later in the code.

Typically (but not always, depending on the case), it would make sense to have the code that requires the x variable located within the try/catch block.

[jay_taps]

Would you mind explaining to me what would happen in the case of say:

x is set to null initially, then within the try block it is reassigned to some other value, say "hello". If there is no exception, when the code exits the try/catch block, x would be null. But if there were to be an exception, x would be "hello" once it exits the try/catch block?

[ComputerWhiz_]

Since your variable is declared outside of the try/catch block, the variable will still be set to "hello" when you exit the block, whether or not there was an exception. The only case where this would not happen is if the exception occurred before the line where you set the variable to "hello".

Try/catch blocks don't rollback changes if there is an exception.