missing return statment in java program help me

[ajay_tabbu]

class Rev
 {
  char a[];
  char i=3; 
    void str()
    {
     for(i='A';i<'D';i++)
      {
       a[i]='i';
       }
     }    
   void show()
    {
     for(int i='A';i<'D';i++)
     {
      System.out.print(a[i]);
      }
     }  
    Void reversStr()
    { 
     for(i='A';i<'D';i++)
     { 
      System.out.print(a[i]);
      }
     }
 }
class Revers
{
  public static void main(String[] args)
   {
    Rev a1=new Rev();
    a1.str();
    a1.show();
    a1.reversStr();
   }
 }

[masijade]

The only thing I can see, at a quick glance is on line 19. Take a close look at that Line.

[ajay_tabbu]

thanks i have slove my problem & my program is compiled.but on run that i have message "Exception in thread "main" java.lang.NullPointer Exception"

[ajay_tabbu]

1. class Rev
2. {
3. char a[];
4. char i=3;
5. void str()
6. {
7. for(i='A';i<'D';i++)
8. {
9. a='i';
   
10. }
11. }
12. void show()
13. {
14. for(int i='A';i<'D';i++)
15. {
16. System.out.print(a);
    
17. }
18. }
19. void reversStr()
20. {
21. for(i='A';i<'D';i++)
22. {
23. System.out.print(a);
    
24. }
25. }
26. }
27. class Revers
28. {
29. public static void main(String[] args)
30. {
31. Rev a1=new Rev();
32. a1.str();
33. a1.show();
34. a1.reversStr();
35. }
36. }
37. plz run and solve the problem

What is the significance of i < 'D'?