a final Q

[Mike Lin]

class newnew{
static int i;
static final int j;
final intk;
public newnew(){
i=1;
j=2;
k=3;
}
}
The compiler will complain "cannot assign a value to final variable j",but k is ok,why?

[John Paverd]

j is declared static, which means that it is associated with the newnew class, and not any particular instance of newnew. It must be initialized when the class is loaded, like this:
static {j = 2;}
or static final int j = 2;
k is not static and thus each instance of newnew has its own k, which can be initialized in the constructor.

[Keen Chen]

1. u can't use a static var in ur constructor;
2. here k is a "blank final", java permit u assign a value to it when runtime, once assigned it, can't change in this instance. so every instance can have a final var k, which is not equal. because u can init it at constructor.
3.static vars only one per class ,no matter how many instances were produced.
btw: are u a Chinese? me too
may be we can chat in Chinese.

[Mike Lin]

But ,i is also a static ,why we can assign a value to i in the class constructor.

[Roan Nicolas]

Remember that final static variables are commonly used to define CONSTANTS. Their purpose is that once defined they should not be change. For example, the constant Integer.MIN_VALUE is declared as final static.
Hope that makes sense.

[John Paverd]

j is final, which means it can only be assigned a value once, and never changed.
i is not final, so you can assign a new value to i as often as you want.
Imagine the following code being executed:
newnew n1 = new newnew();
newnew n2 = new newnew();
Java would assign a value to j twice, which is illegal, because j is final. Both n1 and n2 share the same j, because j belongs to the class, not the instances of the class.

[Mike Lin]

o,i know now .Thank you all very much. :-)