There is no difference in functionality between the two BUT the second listing follows standard Java naming conventions so is prefered. It is also good practice to use indentation to improve readability of code.

1. class Aclass{
2.       int x,y;
3. 
   
4.       Aclass(int x, int y){
5.             this.x = x;
6.             this.y = y;
7.       }    
8. 
   
9. }

There is no difference. They do exactly the same thing.

Some people prefer to write it like the first example, others like the second example.

Personally I always use the second way of writing it, but as said, it's just personal preference.