reverse an integer

[nitin ratra]

1234
how do i reverse this integer without in the simplest way

[nitin ratra]

sorry I posted this on servlets I should have posted it on beginners

[Garrett Rowe]

Here's one way (some details have been omitted).

public List<Integer> intToList(int i) {
  throw new UnsupportedOperationException("TODO: implement this method");
  return null;
}
 
public int listToInt(List<Integer> list) {
   throw new UnsupportedOperationException("TODO: implement this method");
   return null;
}
 
public static void main(String[] args) {
   final int forward = 1234
   final List<Integer> intList = intToList(forward)
   Collections.reverse(intList)
   final int backward = listToInt(intList);
}

[ August 23, 2008: Message edited by: Garrett Rowe ]
[ August 23, 2008: Message edited by: Garrett Rowe ]

[Jesper de Jong]

There's an easier way than what Garrett suggests. Hint: Look at the API documentation of class StringBuilder (or StringBuffer if you're using Java 1.4 or older) and see if there's a method there that you can use.

[SaurabhSri Sri]

Hi,

Try This -

    
StringBuffer rev [deleted] ;

[edit]Deleted part of the solution. CR[/edit]
[ August 23, 2008: Message edited by: Campbell Ritchie ]

[Campbell Ritchie]

Please don't go giving out answers like that, SaurabhSri Sri. Read this FAQ. Nitin will learn lots more if you do as Garrett did, leaving out part of the solution to be worked out. I have felt obliged to delete part of your post.

By the way: Use StringBuilder rather than StringBuffer unless you are constrained to use Java 1.4.2 or older.

[Campbell Ritchie]

Another way is to set up a recursion using the integer divide / and remainder % operations. I would prefer that way for an exercise myself.

[Campbell Ritchie]

I failed to get a recursion to work, but it is easy with a while loop and the / and % operators.

[Pravin Johnson]

Use this code to reverse an integer..

class reverse
{
[removed - DOM]
}
[Please see Campbell's post above. - Dave]
[ August 23, 2008: Message edited by: David O'Meara ]

[David O'Meara]

Originally posted by Campbell Ritchie:
Another way is to set up a recursion using the integer divide / and remainder % operations. I would prefer that way for an exercise myself.

This would be my approach, but I like the String based soluions too.

[Hendy Setyo Mulyo]

The String based solution is definitely the easiest. It suits more if you want to reverse a very very long number such as 12345678901123456656795943456989767. That kind of very very long number is cannot be handled by any Java numeric data type.

[Campbell Ritchie]

Originally posted by Hendy Setyo Mulyo:
12345678901123456656795943456989767. That kind of very very long number is cannot be handled by any Java numeric data type.

I shall have to try it with BigInteger.

[Pat Farrell]

Originally posted by Campbell Ritchie:
Another way is to set up a recursion using the integer divide / and remainder % operations. I would prefer that way for an exercise myself.

In the old Tenex world, that was a common code sample fragment. At first, it was called "decout" (for decimal out) and you could change the constant that you do the div and mod by to convert it to octal, hex, etc.

later jargon file called it yornp for Ye Olde Recursive Number Printer.

Anyone claiming to speak PDP-10, Tenex, TOPS-10 or TOPS-20 was expected to know it by heart.

[nitin ratra]

Thankyou everyone,hope I have asked the question in the right way this time.

[Campbell Ritchie]

Originally posted by Campbell Ritchie:
I failed to get a recursion to work, but it is easy with a while loop and the / and % operators.

Got it, with recursion. Nitin, have you got it to work; you are the one person who is allowed to show a complete answer.