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我正在阅读 Vaadin 教程并遇到了这段代码。但是我无法理解clone在这种情况下的目的。谁能解释一下？

/**
 * Persists or updates customer in the system. Also assigns an identifier for
 * new Customer instances.
 *
 * @param entry
 */
public synchronized void save(Customer entry) {
    if (entry == null) {
        LOGGER.log(Level.SEVERE,
            "Customer is null. Are you sure you have connected your form to the application as described in tutorial chapter 7?");
        return;
    }
    if (entry.getId() == null) {
        entry.setId(nextId++);
    }
    try {
        entry = (Customer) entry.clone();
    } catch (Exception ex) {
        throw new RuntimeException(ex);
    }
    contacts.put(entry.getId(), entry);
}

/**
 * Sample data generation
 */
public void ensureTestData() {
    if (findAll().isEmpty()) {
        final String[] names = new String[] { "Gabrielle Patel", "Brian Robinson", "Eduardo Haugen",
            "Koen Johansen", "Alejandro Macdonald", "Angel Karlsson", "Yahir Gustavsson", "Haiden Svensson",
            "Emily Stewart", "Corinne Davis", "Ryann Davis", "Yurem Jackson", "Kelly Gustavsson",
            "Eileen Walker", "Katelyn Martin", "Israel Carlsson", "Quinn Hansson", "Makena Smith",
            "Danielle Watson", "Leland Harris", "Gunner Karlsen", "Jamar Olsson", "Lara Martin",
            "Ann Andersson", "Remington Andersson", "Rene Carlsson", "Elvis Olsen", "Solomon Olsen",
            "Jaydan Jackson", "Bernard Nilsen" };
        Random r = new Random(0);
        for (String name : names) {
            String[] split = name.split(" ");
            Customer c = new Customer();
            c.setFirstName(split[0]);
            c.setLastName(split[1]);
            c.setStatus(CustomerStatus.values()[r.nextInt(CustomerStatus.values().length)]);
            c.setBirthDate(LocalDate.now().minusDays(r.nextInt(365 * 100)));
            save(c);
        }
    }
}

注意：Customer具有以下数据成员：private Long id, private String firstName = "", private String lastName = "", private LocalDate birthDate, private CustomerStatus status, private String email = ""

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1 回答 1

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您的save方法是公开的，因此可以从任何地方调用。如果有人保存了一个客户，然后又更改了他们保存的客户对象，那么您不希望新的更改反映在您所拥有的内容中contacts。在那里保存克隆可确保您不受他们所做的事情的影响。

但是假设 save 方法不是从 以外的任何地方调用的ensureTestData()，我们还需要克隆它吗？

从技术上讲，短期内没有。无论您的ensureTestData方法是保存它创建的客户还是复制它的客户，都没有区别。但是，在这种情况下，您需要将save方法声明为私有，否则您将不知道何时有人从某个地方引入了对它的调用。在许多情况下，仍然会克隆以防止将来对代码的更改造成不必要的影响。

于 2019-02-19T10:04:18.847 回答