Secret

import java.util.Random;

public class SecretTest {
    public static void main(String[] args) {
        Secret hush = new Secret("What happened yesterday?");
        System.out.println("Original Message: " + hush);
        hush.encrypt();
        System.out.println("Encrypted Message: " + hush);
        hush.decrypt();
        System.out.println("Unencrypted Message: " + hush);
    }
}

//
interface Encryptable {
    public void encrypt();

    public String decrypt();
}

class Secret implements Encryptable {
    private String message;
    private boolean encrypted;
    private int shift;
    private Random generator;

    public Secret(String message) {
        this.message = message;
        this.encrypted = false;
        this.generator = new Random();
        this.shift = this.generator.nextInt(10) + 5;
    }

    public void encrypt() {
        if (!encrypted) {
            String masked = "";
            for (int i = 0; i < message.length(); i++) {
                masked = masked + (char) (message.charAt(i) + shift);
            }

            message = masked;
            encrypted = true;
        }
    }

    public String decrypt() {
        if (encrypted) {
            String unmasked = "";
            for (int i = 0; i < message.length(); i++) {
                unmasked = unmasked + (char) (message.charAt(i) - shift);
            }
            message = unmasked;
            encrypted = false;
        }
        return message;
    }

    public boolean isEncrypted() {
        return encrypted;
    }

    @Override
    public String toString() {
        return message;
    }
}