Comparing Class Types in Java

Question

I want to compare the class type in Java   I thought I could do this   class MyObject 1    class MyObject 2 extends MyObject 1     public boolean function MyObject 1 obj       if obj getClass      MyObject 2 class  System out println  true        I wanted to compare in case if the obj passed into the function was extended from MyObject 1 or not  But this doesn t work  It seems like the getClass   method and the  class gives different type of information   How can I compare two class type  without having to create another dummy object just to compare the class type

User · Answer

As said earlier  your code will work unless you have the same classes loaded on two different class loaders  This might happen in case you need multiple versions of the same class in memory at the same time  or you are doing some weird on the fly compilation stuff  as I am    In this case  if you want to consider these as the same class  which might be reasonable depending on the case   you can match their names to compare them   public static boolean areClassesQuiteTheSame Class lt   gt  c1  Class lt   gt  c2         TODO handle nulls maybe    return c1 getCanonicalName   equals c2 getCanonicalName         Keep in mind that this comparison will do just what it does  compare class names  I don t think you will be able to cast from one version of a class to the other  and before looking into reflection  you might want to make sure there s a good reason for your classloader mess

User · Answer

Check Class java source code for equals    public boolean equals Object obj      return this    obj

User · Answer

If you don t want to or can t use instanceof  then compare with equals    if obj getClass   equals MyObject class   System out println  true      BTW - it s strange because the two Class instances in your statement really should be the same  at least in your example code  They may be different if    the classes have the same short name but are defined in different packages the classes have the same full name but are loaded by different classloaders

User · Answer

Comparing an object with a class using instanceOf or     is already answered   If you have two objects and you want to compare their types with each other  you can use   if  obj1 getClass      obj2 getClass            Both have the same type

User · Answer

Try this   MyObject obj   new MyObject    if obj instanceof MyObject  System out println  true       true   Because of inheritance this is valid for interfaces  too   class Animal    class Dog extends Animal         Dog obj   new Dog    Animal animal   new Dog    if obj instanceof Animal  System out println  true       true if animal instanceof Animal  System out println  true       true if animal instanceof Dog  System out println  true       true   For further reading on instanceof  http   mindprod com jgloss instanceof html

User · Answer

Hmmm    Keep in mind that Class may or may not implement equals   -- that is not required by the spec  For instance  HP Fortify will flag myClass equals myOtherClass

User · Answer

It prints true on my machine  And it should  otherwise nothing in Java would work as expected   This is explained in the JLS  4 3 4 When Reference Types Are the Same   Do you have multiple classloaders in place     Ah  and in response to this comment      I realise I have a typo in my   question  I should be like this    MyImplementedObject obj   new MyImplementedObject     if obj getClass      MyObjectInterface class  System out println  true         MyImplementedObject implements   MyObjectInterface So in other words  I   am comparing it with its implemented   objects    OK  if you want to check that you can do either   if MyObjectInterface class isAssignableFrom obj getClass       or the much more concise  if obj instanceof MyobjectInterface

User · Answer

If you had two Strings and compared them using    by calling the getClass   method on them  it would return true  What you get is a reference on the same object  This is because they are both references on the same class object  This is true for all classes in a java application  Java only loads the class once  so you have only one instance of a given class at a given time  String hello     quot Hello quot   String world    quot world quot    if  hello getClass      world getClass          System out println  quot true quot         prints true

[java] Comparing Class Types in Java

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