Check if a Class Object is subclass of another Class Object in Java

Question

I m playing around with Java s reflection API and trying to handle some fields  Now I m stuck with identifying the type of my fields  Strings are easy  just do myField getType   equals String class   The same applies for other non-derived classes  But how do I check derived classes  E g  LinkedList as subclass of List  I can t find any isSubclassOf      or extends      method  Do I need to walk through all getSuperClass   and find my supeclass by my own

User · Answer

A recursive method to check if a Class lt   gt  is a sub class of another Class lt   gt       Improved version of  To Kra s answer    protected boolean isSubclassOf Class lt   gt  clazz  Class lt   gt  superClass        if  superClass equals Object class                Every class is an Object          return true            if  clazz equals superClass             return true        else           clazz   clazz getSuperclass               every class is Object  but superClass is below Object         if  clazz equals Object class                    we ve reached the top of the hierarchy  but superClass couldn t be found              return false                       try the next level up the hierarchy          return isSubclassOf clazz  superClass

User · Answer

This is an improved version of  schuttek s answer  It is improved because it correctly return false for primitives  e g  isSubclassOf int class  Object class     false  and also correctly handles interfaces  e g  isSubclassOf HashMap class  Map class     true    static public boolean isSubclassOf final Class lt   gt  clazz  final Class lt   gt  possibleSuperClass        if  clazz    null    possibleSuperClass    null                return false            else if  clazz equals possibleSuperClass                 return true            else               final boolean isSubclass   isSubclassOf clazz getSuperclass    possibleSuperClass            if   isSubclass  amp  amp  clazz getInterfaces      null                        for  final Class lt   gt  inter   clazz getInterfaces                                  if  isSubclassOf inter  possibleSuperClass                                         return true                                                     return isSubclass

User · Answer

This works for me   protected boolean isTypeOf String myClass  Class lt   gt  superClass        boolean isSubclassOf   false      try           Class lt   gt  clazz   Class forName myClass           if   clazz equals superClass                 clazz   clazz getSuperclass                isSubclassOf   isTypeOf clazz getName    superClass             else               isSubclassOf   true                   catch ClassNotFoundException e               Ignore              return isSubclassOf

User · Answer

You want this method   boolean isList   List class isAssignableFrom myClass     where in general  List  above  should be replaced with superclass and myClass should be replaced with subclass  From the JavaDoc      Determines if the class or interface represented by this Class object is either the same as  or is a superclass or superinterface of  the class or interface represented by the specified Class parameter  It returns true if so  otherwise it returns false  If this Class object represents a primitive type  this method returns true if the specified Class parameter is exactly this Class object  otherwise it returns false    Reference    Class isAssignableFrom Class      Related   a  Check if an Object is an instance of a Class or Interface  including subclasses  you know at compile time   boolean isInstance   someObject instanceof SomeTypeOrInterface    Example   assertTrue Arrays asList  a    b    c   instanceof List lt   gt      b  Check if an Object is an instance of a Class or Interface  including subclasses  you only know at runtime   Class lt   gt  typeOrInterface      acquire class somehow boolean isInstance   typeOrInterface isInstance someObject     Example   public boolean checkForType Object candidate  Class lt   gt  type       return type isInstance candidate

User · Answer

Inheritance      class A         int i   10        public String getVal             return  I m  A                       class B extends A         int j   20        public String getVal             return  I m  B                       class C extends B           int k   30          public String getVal               return  I m  C                        Methods      public static boolean isInheritedClass Object parent  Object child          if  parent    null    child    null            return false          else           return isInheritedClass parent getClass    child getClass                        public static boolean isInheritedClass Class lt   gt  parent  Class lt   gt  child          if  parent    null    child    null            return false          else           if  parent isAssignableFrom child                  is child or same class           return parent isAssignableFrom child getSuperclass               else             return false                               Test the code      System out println  isInheritedClass new A    new B        isInheritedClass new A    new B          System out println  isInheritedClass new A    new C        isInheritedClass new A    new C          System out println  isInheritedClass new A    new A        isInheritedClass new A    new A          System out println  isInheritedClass new B    new A        isInheritedClass new B    new A            System out println  isInheritedClass A class  B class      isInheritedClass A class  B class        System out println  isInheritedClass A class  C class      isInheritedClass A class  C class        System out println  isInheritedClass A class  A class      isInheritedClass A class  A class        System out println  isInheritedClass B class  A class      isInheritedClass B class  A class        Result       isInheritedClass new A    new B    true     isInheritedClass new A    new C    true     isInheritedClass new A    new A    false     isInheritedClass new B    new A    false     isInheritedClass A class  B class  true     isInheritedClass A class  C class  true     isInheritedClass A class  A class  false     isInheritedClass B class  A class  false

User · Answer

Another option is instanceof   Object o      if  o instanceof Number      double d     Number o  doubleValue      this cast is safe

User · Answer

In addition to  To-kra s answer  If someone doesn t like recurrence      public static boolean isSubClassOf Class lt   gt  clazz  Class lt   gt  superClass            if Object class equals superClass                 return true                     for    Object class equals clazz   clazz   clazz getSuperclass                  if clazz getSuperclass   equals superClass                     return true                                   return false         NOTE  no null checking for clarity

User · Answer

instanceof works on instances  i e  on Objects  Sometimes you want to work directly with classes  In this case you can use the asSubClass method of the Class class  Some examples   1       Class o Object class      Class c Class forName  javax swing JFrame   asSubclass o     this will go through smoothly because JFrame is subclass of Object  c will contain a Class object representing the JFrame class   2       Class o JButton class      Class c Class forName  javax swing JFrame   asSubclass o     this will launch a java lang ClassCastException because JFrame is NOT subclass of JButton  c will not be initialized   3       Class o Serializable class      Class c Class forName  javax swing JFrame   asSubclass o     this will go through smoothly because JFrame implements the java io Serializable interface  c will contain a Class object representing the JFrame class   Of course the needed imports have to be included

[java] Check if a Class Object is subclass of another Class Object in Java

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