Java 中是否有任何类似于 C# 的“AS”关键字的关键字
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Is there any keyword in Java which is similar to the 'AS' keyword of C#
提问by Anubhav Ranjan
As we know C# provides an AS keyword which automatically performs a check whether the Object is of a type and if it is, it then casts it to the needed type else gives a null.
正如我们所知，C# 提供了一个 AS 关键字，它会自动检查对象是否属于某种类型，如果是，则将其强制转换为所需的类型，否则返回 null。
public class User
public class User
{
{
}
}
....
....
Object obj = someObj;
Object obj = someObj;
User user = obj As User;
User user = obj As User;
...
...
Here in the above example, An Object obj can be of type User or some other type. The user will either get an object of type User or a null. This is because the As keyword of C# first performs a check and if possible then performs a casting of the object to the resulting type.
在上面的示例中，对象 obj 可以是 User 类型或其他类型。用户将获得一个 User 类型的对象或一个 null。这是因为 C# 的 As 关键字首先执行检查，然后在可能的情况下将对象强制转换为结果类型。
So is there any keyword in Java which is equivalent to the AS keyword of C#?
那么Java中是否有与C#的AS关键字等价的关键字呢？
回答by Peter Lawrey
You can create a helper method
您可以创建一个辅助方法
public static T as(Object o, Class<T> tClass) {
return tClass.isInstance(o) ? (T) o : null;
}
User user = as(obj, User.class);
回答by jberg
no, you can check with instanceofand then cast if it matches
不，您可以检查instanceof然后投射是否匹配
User user = null;
if(obj instanceof User) {
user = (User) obj;
}
回答by trutheality
No keyword, but for completeness I'll give you the 1-liner equivalent:
没有关键字，但为了完整起见，我会给你 1-liner 等价物：
User user = obj instanceof User ? (User) obj : null;
(You might not have to have the explicit cast, I'm not sure.)
（您可能不必进行明确的演员表，我不确定。）
