My Source

import java.util.*;
public class JavaApplication3 {


    public static void main(String[] args) {
        String SubPalabra1="";
        String SubPalabra2="";
        String Correcta="";

        String Verdadera="";
        int menor;
        String resto="";
        Scanner D=new Scanner(System.in);
        String palabra=D.nextLine().trim();
        if(palabra.length()!=1){
            for(int i=0;i<palabra.length();i++){
                Verdadera="";
                resto=palabra.substring(i+1, palabra.length());
                if(resto.indexOf(palabra.charAt(i))!=-1){
                    SubPalabra1=""+palabra.charAt(i)+resto.substring(0,resto.length());
                      SubPalabra2=""+resto.substring(resto.indexOf(palabra.charAt(i)),resto.length());
                    if(SubPalabra1.length()<SubPalabra2.length()){
                        menor=SubPalabra1.length();
                    }
                    else{
                        menor=SubPalabra2.length();
                    }
                    for(int j=0;j<menor;j++){

                        if(SubPalabra1.charAt(j)==SubPalabra2.charAt(j)){
                            Verdadera=Verdadera+SubPalabra1.charAt(j);
                            if(Verdadera.length()>Correcta.length()){
                                Correcta=Verdadera;
                            }
                        }
                        else{
                            j=menor;
                        }
                    }
                }

            }
        }
        else{
            System.out.println(palabra);
        }
        System.out.println(Correcta);


    }
}

Who is the word that no work?

Here is a bunch of c program which one should practice before directly jumping in strings processing programs.
http://www.techcrashcourse.com/2014/10/c-program-reverse-string.html
http://www.techcrashcourse.com/2014/10/c-program-compare-two-strings.html
http://www.techcrashcourse.com/2014/10/c-program-concatenate-strings.html
http://www.techcrashcourse.com/2014/10/c-program-find-palindrome-string.html