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Need to reverse a string in Java

Posted on 2008-10-20
9
Medium Priority
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Last Modified: 2012-05-05
Hi Folks,

I need an easy way to reverse a string in java, but not character by character, but separated by a fullstop.

For example .. I need

127.0.0.2
to be reversed to
2.0.0.127

Another example

192.168.0.1
to be reversed to
1.0.168.192

Any help would be much appreciated.

Cheers.
0
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Question by:JigsawTech
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9 Comments
 
LVL 24

Expert Comment

by:sciuriware
ID: 22756462
Easiest:  split into numbers,
reverse the numbers,
rebuild the string.

;JOOP!
0
 
LVL 24

Accepted Solution

by:
sciuriware earned 2000 total points
ID: 22756485
String original = "127.0.0.2";

String[] k = original.split("\\.");

String new = k[3] + '.' + k[2] + '.' + k[1] + '.' + k[0];

;JOOP!
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LVL 1

Expert Comment

by:grahamcorp
ID: 22756589
I would imagine you could break this into smaller substrings based on the '.'?
So for example,
Sorry if the syntax etc isn't right, but hopefully you get the idea?
May not be most efficient solution.

String ip = '192.168.0.1';
 
String [] tempIP = ip.split('.');
 
public static string reverseJoin( String[] ip, String delimiter)
{
   ip = reverseArray(ip);
 
   StringBuffer buffer = new StringBuffer();
   Iterator iter = ip.iterator();
 
   while(iter.hasNext())
   {
      buffer.append(iter.next());
      if( iter.hasNext() )
      {
          buffer.append(delimiter)
      }
   }
   return buffer.toString();
}
 
private static reverseArray(String [] arrayToReverse)
{
   String [] tempArray;
 
   for( int i = 0; i < tempIP.length; i++ )
   {
      tempArray[i] = tempIP[tempIP.length-i];
   }
   
   return tempArray;
}

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0
 
LVL 1

Expert Comment

by:grahamcorp
ID: 22756601
I wasn't sure if the ip thing was just an example, i.e. is the string also going to be in the format <num>.<num>.<num>.<num>?
If it is then sciuriware is a better solution than mine as mine will be overkill.
0
 
LVL 9

Expert Comment

by:darkapple
ID: 22756685
Ok here is a function i've created to reverse string as per your requirement.
	private String strRev(String str){
		
		String rev = "";
 
		String[] k = str.split("\\.");
		
 
		for(int i=k.length; i!=0; i--){
			
			rev = rev.concat(k[i-1]);
			rev = ((i-1)>0?rev.concat("."):rev.concat(""));
		}
 
		return rev;
	}

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0
 
LVL 1

Author Closing Comment

by:JigsawTech
ID: 31507777
Thanks alot, works great.
0
 
LVL 1

Author Comment

by:JigsawTech
ID: 22756745
hi folks,

Appreciate the speedy responses .. didn't even think about using split..  doh.

Thanks again.
0
 
LVL 24

Expert Comment

by:sciuriware
ID: 22756951
Have a good time with avaJ.

!POOJ;
0

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