every object reference variable must refer to some objectunless it is nullin which case it points to nothing using the remote control analogya null reference is remote control holder that is empty initiallyunless we assign an object variable to point to somethingit is null there canin factbe many references to the same objectand each reference to specific object can be used to call methods on that object such situation would correspond to our having many remote controls that all work on the same device any of the remotes can be used to make change to the device (like changing channel on televisionnote that if one remote control is used to change the devicethen the (singleobject pointed to by all the remotes changes likewiseif we use one object reference variable to change the state of the objectthen its state changes for all the references to it this behavior comes from the fact that there are many referencesbut they all point to the same object one of the primary uses of an object reference variable is to access the members of the class for this objectan instance of its class that isan object reference variable is useful for accessing the methods and instance variables associated with an object this access is performed with the dot ("operator we call method associated with an object by using the reference variable namefollowing that by the dot operator and then the method name and its parameters this calls the method with the specified name for the object referred to by this object reference it can optionally be passed multiple parameters if there are several methods with this same name defined for this objectthen the java runtime system uses the one that matches the number of parameters and most closely matches their respective types method' name combined with the number and types of its parameters is called method' signaturefor it takes all