Voici le Code:

import java.io.*;

class Alphabet{

public static void main(String args[])throws IOException{

String s;

char b,ch;

int d=0,c=0,i,l,p=0,k;

InputStreamReader x=new InputStreamReader(System.in);

BufferedReader y=new BufferedReader(x);

System.out.println("Entrez une chaine");

s=y.readLine();

s=s.toLowerCase();

s=s.concat(" ");

l=s.length();

for(k=97;k<122;k++){

for(i=0;i<l;i++){

b=s.charAt(i);

if(b!=' '){

d=d+1;

}

else{

ch=s.charAt(i-d);

c=(int)ch;

if(c==k){

p=i-d;

System.out.print(s.substring(p,i)+" ");

}

d=0;

} } } } }