getClass() 方法
getClass()
方法可用于查找对象的运行时类类型。请参阅以下示例:
public class User {
private long userID;
private String name;
public User(long userID, String name) {
this.userID = userID;
this.name = name;
}
}
public class SpecificUser extends User {
private String specificUserID;
public SpecificUser(String specificUserID, long userID, String name) {
super(userID, name);
this.specificUserID = specificUserID;
}
}
public static void main(String[] args){
User user = new User(879745, "John");
SpecificUser specificUser = new SpecificUser("1AAAA", 877777, "Jim");
User anotherSpecificUser = new SpecificUser("1BBBB", 812345, "Jenny");
System.out.println(user.getClass()); //Prints "class User"
System.out.println(specificUser.getClass()); //Prints "class SpecificUser"
System.out.println(anotherSpecificUser.getClass()); //Prints "class SpecificUser"
}
getClass()
方法将返回最具体的类类型,这就是为什么在 anotherSpecificUser
上调用 getClass()
时,返回值为 class SpecificUser
,因为它比继承树低于 User
。
值得注意的是,虽然 getClass
方法被声明为:
public final native Class<?> getClass();
调用 getClass
返回的实际静态类型是 Class<? extends T>
,其中 T
是调用 getClass
的对象的静态类型。
即以下将编译:
Class<? extends String> cls = "".getClass();