我正在阅读Vaadin教程，并遇到了这段代码。但是，我无法理解clone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 = ""
您的save方法是公开的，因此可以在任何地方调用。如果某人保存了一个客户，后来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。将副本保存在此处可确保您不受其行为的影响。
但是，假设没有从其他地方调用save方法
ensureTestData()，是否还需要克隆它？
从技术上来说，近视没有。您的ensureTestData方法是保存它创建的客户还是该方法的克隆都没有区别。但是，在那种情况下，您将需要将save方法声明为私有，否则您将不知道何时有人从某个地方对其进行调用。在许多情况下，仍然会克隆以防止将来对代码进行更改而引起不良影响。
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