Check if an object belongs to a class in Java

Question

Is there an easy way to verify that an object belongs to a given class  For example  I could do  if a getClass      new MyClass    getClass            do something     but this requires instantiating a new object on the fly each time  only to discard it  Is there a better way to check that  a  belongs to the class  MyClass

User · Answer

The usual way would be   if  a instanceof A    However  there are cases when you can t do this  such as when A in a generic argument    Due to Java s type erasure  the following won t compile    lt A gt  boolean someMethod Object a        if  a instanceof A              and the following won t work  and will produce an unchecked cast warning     lt A gt  void someMethod Object a        try           A casted    A a            catch  ClassCastException e                           You can t cast to A at runtime  because at runtime  A is essentially Object   The solutions to such cases is to use a Class instead of the generic argument   void someMethod Object a  Class lt A gt  aClass        if  aClass isInstance a            A casted   aClass cast a                        You can then call the method as   someMethod myInstance  MyClass class   someMethod myInstance  OtherClass class

User · Answer

Try operator instanceof

User · Answer

I agree with the use of instanceof already mentioned   An additional benefit of using instanceof is that when used with a null reference instanceof of will return false  while a getClass   would throw a NullPointerException

User · Answer

The instanceof keyword  as described by the other answers  is usually what you would want   Keep in mind that instanceof will return true for superclasses as well    If you want to see if an object is a direct instance of a class  you could compare the class  You can get the class object of an instance via getClass    And you can statically access a specific class via ClassName class   So for example   if  a getClass      X class         do something     In the above example  the condition is true if a is an instance of X  but not if a is an instance of a subclass of X   In comparison   if  a instanceof X           do something       In the instanceof example  the condition is true if a is an instance of X  or if a is an instance of a subclass of X   Most of the time  instanceof is right

User · Answer

If you ever need to do this dynamically  you can use the following  boolean isInstance Object object  Class lt   gt  type        return type isInstance object      You can get an instance of java lang Class by calling the instance method Object  getClass on any object  returns the Class which that object is an instance of   or you can do class literals  for example  String class  List class  int   class   There are other ways as well  through the reflection API  which Class itself is the entry point for

User · Answer

Use the instanceof operator   if a instanceof MyClass          do something

[java] Check if an object belongs to a class in Java

Examples related to java

Examples related to polymorphism