Why am I receiving a "non static variable" error when calling this Java class?

Question

Receiving error non static variable this cannot be referenced from a static context when compiling the following code; what is the problem?

class bwCalc {
    class Tst{
     public void tst() {
         byte[] data = new byte[1024];//1 kb buffer
         int count;
         long startedAt = System.currentTimeMillis();
         while((System.currentTimeMillis()-startedAt)<1) {
             System.out.println("hello\n");
         }

     }
 }
 public static void main(String argc[]) {
     Tst c = new Tst();
     c.tst();  
 }
}

your exact error - http://stackoverflow.com/questions/7638169/non-static-variable-this-cannot-be-referenced-from-a-static-context — djechlin, Feb 22 '13 at 18:32

score 4 · Answer 1 · answered Feb 22 '13 at 18:32

4

You need the Outer class instance.

bwCalc  b = newbwCalc ();     
     Tst c = b.new Tst();
         c.tst();

Or simply make the inner class static.

answered Feb 22 '13 at 18:32

PermGenError

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score 3 · Answer 2 · answered Feb 22 '13 at 18:32

3

The Tst class should be static, because it's not attached to a particular instance of bwCalc.

answered Feb 22 '13 at 18:32

Louis Wasserman

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so every class declared inside another should be static? – Jinu Joseph Daniel Feb 22 '13 at 18:32
2

not necessarily. depends how you construct the new class – 75inchpianist Feb 22 '13 at 18:33
1

@JinuJD no, unless it shouldn't be - but go read up on this. – djechlin Feb 22 '13 at 18:33
1

@JinuJD Either that or you need an instance of the outer class to instantiate the inner class. – G. Bach Feb 22 '13 at 18:34
1

Every inner class should be static that isn't associated with an instance of the outer class. – Louis Wasserman Feb 22 '13 at 18:38
k i got the idea..since variables in static context are instantiated at the start of program,variables inside main() will be instantiated at start .Tst is a sub class of bwCalc .bwCalc is not at all instatiated.So i cannot create instatnce of Tst.Is it? – Jinu Joseph Daniel Feb 22 '13 at 18:39
1

no, Tst is not a subclass, it is an inner class. a subclass is a separate class that inherits from a superclass. it would be declared in a separate file as public class Tst extends BwCalc. the issue with inner classes is that they may exist after the outer class object is destroyed, they have to be static to allow this to happen – Jeff Hawthorne Feb 22 '13 at 19:10
k...got it....................... – Jinu Joseph Daniel Feb 23 '13 at 10:51

Why am I receiving a "non static variable" error when calling this Java class?

2 Answers2