无法对非静态方法进行静态引用？

Question

我一直收到错误：＆＃34;无法对类型为Encrypt＆＃34;

的非静态方法编码（字符串）进行静态引用

它出现在这一行： encWord = encode（plaintext）;

谁能告诉我发生了什么？我看过类似的问题，继续尝试不同的事情，但没有运气。希望我的代码现在不是太乱了。

public class Encrypt implements MessageEncode {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        String choice;
        String ans;


        System.out.print("Hi\n");
        do{
            String plaintext;
            choice = "";
            ans = "";
            String encWord;
            Scanner keyboard = new Scanner(System.in);

            System.out.print("Which word would you wish to encode or decode?: ");
            plaintext = keyboard.next();
            System.out.print("How far would you like the letters shifted?: ");
            shift = keyboard.nextInt();


            encWord = encode(plaintext);
            System.out.print(plaintext+"\n");

            while(!choice.equals("y") && !choice.equals("n")){
                System.out.print("Would you like to continue? (y or n): ");
                choice = keyboard.next();
            }

            if(choice.equals("y")){
                ans = "y";
                System.out.println("\nOnce more...");
            } else{
                ans = "n";
            }




        }while(ans == "y");

    }

    private static int shift;

    public Encrypt(int shift){
        Encrypt.shift = shift;
    }

    @Override
    public String encode(String plaintext) {
        StringBuffer newtext = new StringBuffer();
        newtext = new StringBuffer(plaintext);
        for(int i=0; i < newtext.length(); i++){
            for(int n=0; n < 25; n++){
                newtext = shifter(newtext, i, n);
            }
        }
        return newtext.toString();
    }

    public StringBuffer shifter(StringBuffer plaintext, int i, int n) {
        char[] letters =
            { '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'
            };
        StringBuffer newtext = new StringBuffer();
        newtext = new StringBuffer(plaintext);

        if(newtext.charAt(i) == letters[n]){
            n += shift;
            newtext.setCharAt(i, letters[n]);

        }


        return newtext;
    }







}

-------------------------------------

//Also, it has an interface:

public interface MessageEncode {

    public abstract String encode(String plaintext);

}