find missing letters in a sentence

import java.util.Scanner;
class yo
{public static void main(String args[]){
String sentence;int len;int i=0;
Scanner in=new Scanner(System.in);
sentence=in.nextLine();
System.out.println("entered sentence is "+sentence);
len=sentence.length();
char alpha[]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
char miss[]=new char[2];System.out.println("length is"+len);
while(i{
{char letter;
letter=sentence.charAt(i);
for(int j=0;j<26;j++)
{if(letter==alpha[j]){alpha[j]=miss[0];}}i++;
}}
System.out.print("missing letters are");
for(i=0;i<26;i++)
{System.out.print(alpha[i]);}
}}