问题
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.
public class User
{
}
....
Object obj = someObj;
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.
So is there any keyword in Java which is equivalent to the AS keyword of C#?
回答1:
You can create a helper method
public static T as(Object o, Class<T> tClass) {
return tClass.isInstance(o) ? (T) o : null;
}
User user = as(obj, User.class);
回答2:
no, you can check with instanceof and then cast if it matches
User user = null;
if(obj instanceof User) {
user = (User) obj;
}
回答3:
No keyword, but for completeness I'll give you the 1-liner equivalent:
User user = obj instanceof User ? (User) obj : null;
(You might not have to have the explicit cast, I'm not sure.)
来源：https://stackoverflow.com/questions/6219773/is-there-any-keyword-in-java-which-is-similar-to-the-as-keyword-of-c-sharp