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Message:

instance initialization vs. field initialization in anonymous inner classes

Posted by Andrew L. Marshall on March 03, 2001 at 2:32 PM

On page 376 of Thinking In Java, 2nd edition, Bruce Eckel gives an example of creating a "constructor" within an anonymous inner class using instance initialization. Now, I do understand what instance initialization is, and I do know what a field variable is, and I do readily concede that Bruce's example code Parcel9.java will not compile without instance initialization.

But I do not understand why instance initialization *must* be used. Why is it that the compiler balks at the "if(cost > 100)" conditional, when, experimentally, I initialize the "cost" variable as a field variable with the value "Math.round(price)", and I do not include the instance-initializing brackets around the conditional?

What's wrong with having a conditional that evaluates a field variable from within an anonymous inner class?

I'm hoping someone will explain this example to me; I'm obviously missing something pretty basic!! Thanks in advance, and I will really appreciate any help people are kind enough to give me...

-Andrew

• Instance initialization Gareth March 05, 2001 at 6:55 AM (0)