Encrypt and decrypt a serializable object
Some obvious problems that jump into the eye:


Don't use duplicate string literals, like "MyDifficultPassw" and "AES/ECB/PKCS5Padding". Put them into constants and define them near the top.
Don't e.printStackTrace(). It's considered bad practice.
The encrypt and decrypt methods violate the single responsibility principle, because they encrypt / decrypt and at the same time do file I/O. Instead of writing to / reading from a filesystem path, it would be better to work with streams. That would open make them testable too (see below).
The decrypt method takes a Serializable object that's not used at all. Also, the initialization SealedObject sealedObject = null; is pointless, as the variable is always assigned before use anyway.


It would be slightly better this way:

private static final byte[] key = "MyDifficultPassw".getBytes();
private static final String transformation = "AES/ECB/PKCS5Padding";

public static void encrypt(Serializable object, OutputStream ostream) throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
    try {
        // Length is 16 byte
        SecretKeySpec sks = new SecretKeySpec(key, transformation);

        // Create cipher
        Cipher cipher = Cipher.getInstance(transformation);
        cipher.init(Cipher.ENCRYPT_MODE, sks);
        SealedObject sealedObject = new SealedObject(object, cipher);

        // Wrap the output stream
        CipherOutputStream cos = new CipherOutputStream(ostream, cipher);
        ObjectOutputStream outputStream = new ObjectOutputStream(cos);
        outputStream.writeObject(sealedObject);
        outputStream.close();
    } catch (IllegalBlockSizeException e) {
        e.printStackTrace();
    }
}

public static Object decrypt(InputStream istream) throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
    SecretKeySpec sks = new SecretKeySpec(key, transformation);
    Cipher cipher = Cipher.getInstance(transformation);
    cipher.init(Cipher.DECRYPT_MODE, sks);

    CipherInputStream cipherInputStream = new CipherInputStream(istream, cipher);
    ObjectInputStream inputStream = new ObjectInputStream(cipherInputStream);
    SealedObject sealedObject;
    try {
        sealedObject = (SealedObject) inputStream.readObject();
        return sealedObject.getObject(cipher);
    } catch (ClassNotFoundException | IllegalBlockSizeException | BadPaddingException e) {
        e.printStackTrace();
        return null;
    }
}


This is only slightly better, it still looks quite messy. But it has the big advantage that now this is testable, for example:

@Test
public void testEncryptDecryptString() throws InvalidKeyException, NoSuchAlgorithmException, NoSuchPaddingException, IOException {
    String orig = "hello";
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    encrypt(orig, baos);
    ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
    assertEquals(orig, decrypt(bais));
}

@Test
public void testEncryptDecryptPerson() throws InvalidKeyException, NoSuchAlgorithmException, NoSuchPaddingException, IOException {
    Person orig = new Person("Jack", 21);
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    encrypt(orig, baos);
    ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
    assertEquals(orig, decrypt(bais));
}

static class Person implements Serializable {
    private static final long serialVersionUID = 0;
    private final String name;
    private final int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        Person person = (Person) o;

        if (age != person.age) {
            return false;
        }
        if (!name.equals(person.name)) {
            return false;
        }

        return true;
    }
    @Override
    public int hashCode() {
        int result = name.hashCode();
        result = 31 * result + age;
        return result;
    }
}