Java newb. Feedback appreciated!

[](/s "import java.util.*;

public class Rovarspraket {

public static void main(String [] args){

    Scanner kb = new Scanner(System.in);

    System.out.println("Encode or decode?");

    String encodeOrDecode = kb.nextLine();

    String check = "bcdfghjklmnpqrstvwxz";

    String input = kb.nextLine();
    String useInput = input;

    if(encodeOrDecode.equalsIgnoreCase("encode")){
        for(int i = 0 ; i < useInput.length() ; i++){
            if(check.contains(""+useInput.toLowerCase().charAt(i))){
                useInput = useInput.substring(0,i)+useInput.charAt(i)+"o"
                        +useInput.toLowerCase().charAt(i)+useInput.substring(i+1);
                i=i+2;
            }
        }
        System.out.println("Original Input: "+input);
        System.out.println("Robber's Language Translation: "+useInput);
    } else if (encodeOrDecode.equalsIgnoreCase("decode")){
        for( int i = 0 ; i < useInput.length() ; i++){
            if(useInput.toLowerCase().charAt(i)=='o' && i!=0 && i!= useInput.length()-1){
                if(useInput.toLowerCase().charAt(i-1)==useInput.toLowerCase().charAt(i+1)){
                    useInput = useInput.substring(0, i)+useInput.substring(i+2);
                }
            }
        }
        System.out.println("Original Input: "+input);
        System.out.println("Robber's Language Translation: "+useInput);
    } else {
        System.out.println("Not a valid option.");
    }
}

} ")