Please explain me this code

Advice:
Learn to indent properly your code, it show its structure and it helps reading and understanding. It also helps spotting structures mistakes.

class test{
  public static void main(String args[]){
    b ref=new b();
    ref.x=99;
    ref.show();
  }
}
class a{
  int x=10;
}
class b extends a{
  void show(){
    a ref=new a();
    System.out.println(super.x);
  }
}
class test{
  public static void main(String args[]){
    b ref=new b();
    ref.x=99;
    ref.show();
  }
}
class a{
  int x=10;
}
class b extends a{
  void show(){
    a ref=new a();
    System.out.println(super.x);
  }
}

Professional programmer's editors have this feature and others ones such as parenthesis matching and syntax highlighting.
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This code will not compile because you pasted the same code 2 times.
The debugger is a tool that allow you to execute your code line by line and to inspect all variables as the program pause.
The debugger is an incredible learning tool, but you_ have to give it a try.