Java 类型安全：List 类型的表达式需要未经检查的转换以符合 List<Object[]>
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Type safety: The expression of type List needs unchecked conversion to conform to List<Object[]>
提问by Hakan Kiyar
Im getting always a type safety warning when I want to start a Hibernate application. Is there a method to get rid of this without using @SuppressWarnings("unchecked")?
当我想启动 Hibernate 应用程序时，我总是收到类型安全警告。有没有一种方法可以在不使用的情况下摆脱这种情况@SuppressWarnings("unchecked")？
here is my Code:
这是我的代码：
Configuration config = new Configuration();
config.addAnnotatedClass(Employee.class);
config.configure("hibernate.cfg.xml");
new SchemaExport(config).create(false, false);
ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
.applySettings(config.getProperties()).build();
SessionFactory factory = config.buildSessionFactory(serviceRegistry);
Session session = factory.getCurrentSession();
session.beginTransaction();
Query q = session
.createQuery("SELECT e.empId,e.empName FROM Employee e");
@SuppressWarnings("unchecked")
List<Object[]> list = q.list(); <-- here is the problem!
采纳答案by Olivier Croisier
Hibernate's Session.list()returns a plain, raw List.
HibernateSession.list()返回一个普通的原始List.
It is perfectly legal Java syntax to cast it to a parameterized collection (List<Object[]>here). But due to the fact that generic type infos are wiped out at runtime, the compiler will emit a warning to tell you it cannot guarantee this cast will actually be valid.
So it's just his way to tell you "Hey, you're playing with fire here, I hope you know what you do, because I don't".
将其强制转换为参数化集合是完全合法的 Java 语法（List<Object[]>此处）。但是由于泛型类型信息在运行时会被清除，编译器会发出警告，告诉你它不能保证这个转换实际上是有效的。所以这只是他告诉你“嘿，你在这里玩火，我希望你知道你在做什么，因为我不知道”的方式。
In this particular case, you can't do anything to eliminate this warning, but you can take the responsibility of explicitely ignoring it by using the @SuppressWarningsannotation.
在这种特殊情况下，您无法采取任何措施来消除此警告，但您可以通过使用@SuppressWarnings注释承担明确忽略它的责任。
回答by nestorishimo10
No, there is no way to remove it unless you make q.list() exactly a List<Object[]>
不，除非您使 q.list() 恰好是一个，否则无法删除它 List<Object[]>
回答by Thomas
You can force the cast to make the warning go away, but much like suppressing the warning it hides a potential issue since q.list() isn't guaranteed to return that exact type.
您可以强制强制转换使警告消失，但就像抑制警告一样，它隐藏了一个潜在的问题，因为 q.list() 不能保证返回那个确切的类型。
List<Object[]> list = (List<Object[]>)q.list();
