How to determine an object s class

Question

If class B and class C extend class A and I have an object of type B or C  how can I determine of which type it is an instance

User · Answer

I use the blow function in my GeneralUtils class  check it may be useful      public String getFieldType Object o        if  o    null            return  Unable to identify the class name             return o getClass   getName

User · Answer

You can use   Object instance   new SomeClass    instance getClass   getName      will return the name  as String       SomeClass   instance getClass      will return the SomeClass  Class object   HTH  But I think most of the time it is no good practice to use that for control flow or something similar

User · Answer

There is also an  isInstance method on the  Class  class  if you get an object s class via myBanana getClass   you can see if your object myApple is an instance of the same class as myBanana via  myBanana getClass   isInstance myApple

User · Answer

You can use getSimpleName    Let s say we have a object  Dog d   new Dog    The we can use below statement to get the class name  Dog  E g   d getClass   getSimpleName       return String  Dog   PS  d getClass   will give you the full name of your object

User · Answer

Any use of any of the methods suggested is considered a code smell which is based in a bad OO design   If your design is good  you should not find yourself needing to use getClass   or instanceof   Any of the suggested methods will do  but just something to keep in mind  design-wise

User · Answer

Use Object getClass     It returns the runtime type of the object

User · Answer

if  obj instanceof C      your code

User · Answer

checking with isinstance   would not be enough if you want to know in run time   use   if someObject getClass   equals C class          do something

User · Answer

I Used Java 8 generics to get what is the object instance at runtime rather than having to use switch case   public  lt T gt  void print T data        System out println data getClass   getName       gt  The data is     data       pass any type of data and the method will print the type of data you passed while calling it  eg      String str    Hello World       int number   10      double decimal   10 0      float f   10F      long l   10L      List list   new ArrayList        print str       print number       print decimal       print f       print l       print list     Following is the output   java lang String   gt  The data is Hello World java lang Integer   gt  The data is 10 java lang Double   gt  The data is 10 0 java lang Float   gt  The data is 10 0 java lang Long   gt  The data is 10 java util ArrayList   gt  The data is

User · Answer

Multiple right answers were presented  but there are still more methods  Class isAssignableFrom   and simply attempting to cast the object  which might throw a ClassCastException    Possible ways summarized  Let s summarize the possible ways to test if an object obj is an instance of type C      Method  1 if  obj instanceof C            Method  2 if  C class isInstance obj             Method  3 if  C class isAssignableFrom obj getClass               Method  4 try       C c    C  obj         No exception  obj is of type C or IT MIGHT BE NULL    catch  ClassCastException e          Method  5 try       C c   C class cast obj          No exception  obj is of type C or IT MIGHT BE NULL    catch  ClassCastException e        Differences in null handling  There is a difference in null handling though    In the first 2 methods expressions evaluate to false if obj is null  null is not instance of anything   The 3rd method would throw a NullPointerException obviously   The 4th and 5th methods on the contrary accept null because null can be cast to any type       To remember  null is not an instance of any type but it can be cast to any type    Notes   Class getName   should not be used to perform an  is-instance-of  test becase if the object is not of type C but a subclass of it  it may have a completely different name and package  therefore class names will obviously not match  but it is still of type C  For the same inheritance reason Class isAssignableFrom   is not symmetric  obj getClass   isAssignableFrom C class  would return false if the type of obj is a subclass of C

User · Answer

We can use reflection in this case  objectName getClass   getName      Example -  protected void doGet HttpServletRequest request  HttpServletResponse response  throws ServletException  IOException        String name   request getClass   getName       In this case you will get name of the class which object pass to HttpServletRequest interface refference variable

[java] How to determine an object's class?

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