why does my code not giving me reverse number accurately

Java Code Example: i am facing issue when i insert 010 it shows only 1 instead of whole number and when i insert 200 it gave me reverse number only 2 while it should show me exact 002 how can i get exact number in reverse:

class Reverse{
    public static void main(String args[]){  
      int remander,sum=0;    
      int number=454;      
      while(n>0) // loop here
      {
           remander=n%10;  // Getting remainder
           sum=(sum*10)+remander;    
           number=number/10;   
      } 
        System.out.println("Reverse"+sum);
    }   
}  

It is clear that you are new to Java, and new to programming. Welcome to StackOverflow. I'm going to add some extra advice that I don't normally offer, to help you get better faster.

1. Don't reuse a variable for more than one thing. Use it for only one thing. That means that if a variable holds you input, don't overwrite it with intermediate values. Variables are (relatively) cheap, create another. You can practice this by marking your variables final which will prevent you from changing their values after assigned.

2. Use meaningful variable names. "r" is not a meaningful name. "remainder" is a meaningful name. This helps others immediately, and will help you later, when the program isn't fresh on your mind and you don't remember what "r" means.

3. Once you master not reusing variables, you will have a lot of variables. Look for variables that are "set once and read once" and try to rearrange your code to remove them completely. It will take some time to understand what I mean, but if you have heard of "refactoring" the idea is to remove the variable name because it isn't used twice (so it probably isn't a key part of your problem.

Now, applying these rules

  final int number = 454;      
  // get the number digits, smallest to largest
  int remainder = number;
  int accumulator = 0;
  while (remainder > 0) {
     final int digit = remainder % 10;
     accumulator = accumulator * 10 + digit;
     remainder = remainder / 10;
  }
  final int reversed = accumulator;

note that digit is never used twice

  final int number = 454;      
  // get the number digits, smallest to largest
  int remainder = number;
  int accumulator = 0;
  while (remainder > 0) {
     accumulator = accumulator * 10 + remainder % 10;
     remainder = remainder / 10;
  }
  final int reversed = accumulator;

Note that all that "logic" could have a really good name put to it, so we'll create a "method"

  public int reverse(int value) {
      int remainder = value;
      int accumulator = 0;
      while (remainder > 0) {
          accumulator = accumulator * 10 + remainder % 10;
          remainder = remainder / 10;
      }
      return accumulator;
  }

which cleans up the other code to

  final int number = 454;
  final int reversed = reverse(number);

or maybe even

  final int reversed = reverse(454);