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[java] 'variable' might not have been initialised

Started by PolyVox Apr 11, 2005 at 4:02 PM 4 replies 1k views

Original Post

Apr 11, 2005 at 4:02 PM

Hi all, This is a pretty basic problem but I'm not used to Java... C++ doesn't force such correctness issues on you! I have some code which (in abstract form) looks something like the following:


Component myComponent;
try
{
//Initialise my component...
myComponent = funtionWhichReturnsComponentSubclass();
}
catch(Exception e)
{
//Scream lots and die
System.exit(1);
}

//Whole lot of code here...
.
.
.

myComponent.doSomething();

At the call to myComponent.doSomething() Java complains that my variable might not of been initialised, presumably because the exception might have been thrown. But in this case i'll have exited and won't care. In other words *I* know it's initialised, even if Java doesn't. Whats the 'correct' approach to this? Should i declare the Compoment with: Component myComponent = new JPanel(); so it's always initialised to something? This is clearly a waste of time as it will get reassigned in the next line anyway. Or does my 'Whole lot of code here' all have to go in the 'try' block. I love Java but just wish it trusted me a bit more!

Optus

Apr 11, 2005 at 5:05 PM

easiest way to get around this would be to declare it null e.g.

Component myComponent = null;

edit: grammar is greater than me

TheBluMage

Apr 12, 2005 at 4:22 AM

I haven't checked, but if I remember correctly, you could also put a return in the catch block right after your System.exit call. Then the compiler should be able to figure out that there's no way it can get to the point where your component is used without it being assigned a value.

PolyVox

Author

PolyVox

Apr 12, 2005 at 6:00 AM

Quote:
Original post by Optus
easiest way to get around this would be to declare it null e.g.

Component myComponent = null;

edit: grammar is greater than me

So is there a difference between initialising to null and not being initialised at all? Besides, i thought in Java varialbes were initialised to null automatically...

Quote:
Original post by TheBluMage
I haven't checked, but if I remember correctly, you could also put a return in the catch block right after your System.exit call. Then the compiler should be able to figure out that there's no way it can get to the point where your component is used without it being assigned a value.

Ah, good idea! I'll give it a try.

Lotuspec

Apr 12, 2005 at 9:24 AM

Quote:
Original post by esuvs

So is there a difference between initialising to null and not being initialised at all? Besides, i thought in Java varialbes were initialised to null automatically...

Only object variables are automatically initialised

ex.

public class myClass {
private Object myVar; // automatically init to null

public myClass() {
Object someVar; // no init
}

CaptainJester

101

CaptainJester

Apr 12, 2005 at 9:30 AM

Only class level variables are initialized to null.(or 0/false for primitives). Method level variables are undefined until assigned a value.

Quote:

At the call to myComponent.doSomething() Java complains that my variable might not of been initialised, presumably because the exception might have been thrown. But in this case i'll have exited and won't care. In other words *I* know it's initialised, even if Java doesn't. Whats the 'correct' approach to this? Should i declare the Compoment with:

How do you know it is initialized. If that try block throws an exception, then it is not initialized. Also System.exit(1) is an API call, not a language feature, so to the compiler it is going to continue down through the code.

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