This java code is for reverse the string but it returning concat null with returned string.

import java.util.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Practice {

    public static void main(String[] args) {
        String str = "";
        try {
            str = reverse("Singh");
        } catch (Exception ex) {
            Logger.getLogger(Practice.class.getName()).log(Level.SEVERE, null, ex);
            System.out.print(ex.getMessage());
        }finally{
            System.out.println(str);
        }

    }
    public static String reverse(String str) throws Exception{
        String temp = null;
        if(str.length()<=0){
            throw new Exception("empty");
        }else{
            for(int i=str.length()-1;i>=0;i--){
                temp+=str.charAt(i);
            }
        }
        return temp.trim();
    }
}

Output:

nullhgniS