java Class isInstance vs Class isAssignableFrom

Question

Let clazz be some Class and obj be some Object   Is  clazz isAssignableFrom obj getClass      always the same as  clazz isInstance obj       If not  what are the differences

User · Answer

For brevity  we can understand these two APIs like below    X class isAssignableFrom Y class    If X and Y are the same class  or X is Y s super class or super interface  return true  otherwise  false    X class isInstance y    Say y is an instance of class Y  if X and Y are the same class  or X is Y s super class or super interface  return true  otherwise  false

User · Answer

clazz isAssignableFrom Foo class  will be true whenever the class represented by the clazz object is a superclass or superinterface of Foo   clazz isInstance obj  will be true whenever the object obj is an instance of the class clazz   That is    clazz isAssignableFrom obj getClass       clazz isInstance obj    is always true so long as clazz and obj are nonnull

User · Answer

I think the result for those two should always be the same  The difference is that you need an instance of the class to use isInstance but just the Class object to use isAssignableFrom

User · Answer

Both answers are in the ballpark but neither is a complete answer   MyClass class isInstance obj  is for checking an instance   It returns true when the parameter obj is non-null and can be cast to MyClass without raising a ClassCastException   In other words  obj is an instance of MyClass or its subclasses   MyClass class isAssignableFrom Other class  will return true if MyClass is the same as  or a superclass or superinterface of  Other   Other can be a class or an interface   It answers true if Other can be converted to a MyClass   A little code to demonstrate   public class NewMain       public static void main String   args                NewMain nm   new NewMain            nm doit               class A          class B extends A          public void doit                 A myA   new A            B myB   new B            A   aArr   new A 0           B   bArr   new B 0            System out println  b instanceof a       myB instanceof A       true         System out println  b isInstance a      A class isInstance myB      true         System out println  a isInstance b      B class isInstance myA      false         System out println  b isAssignableFrom a      A class isAssignableFrom B class      true         System out println  a isAssignableFrom b      B class isAssignableFrom A class      false         System out println  bArr isInstance A      A class isInstance bArr      false         System out println  bArr isInstance aArr      aArr getClass   isInstance bArr      true         System out println  bArr isAssignableFrom aArr      aArr getClass   isAssignableFrom bArr getClass        true

[java] java: Class.isInstance vs Class.isAssignableFrom

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