How can I replace/delete chars from an array?

Hello I need to do a cipher function and I need a result like this: Ex: String "Hello Java" , int 3

Hell
o-Ja
va

And I need to replace the 3 letters in each loop, but allways print the same letters. And I need a way to do it. thanx

public static String cifradoTrans(String phrase, int N){
    String output= "";
    char[] letter= phrase.toCharArray();
    for(int j =0; j<letter.length;j++){        
        for(int i =0; i<N; i++){
            System.out.print(letter[i]);
        }
        System.out.println("");
    }
    return output;
}