Hi friends this is Dattaraya.......:>
Dear Friend Sunny!
If we have declared instance variable as final & we don't initialise it at declaration time then it will be initilised to its default value of data type, after that we can't reinitialise that instance variable,instance variable is always be compile time constant if it declared as final.
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This is the correction of your statement of " instance variables are come under the categories of compile time constant & we can do like this to instance var i.e. final int b;
b=5;"