Question

From what I have learned, the class objects in Java are actually references to those objects. An object itself cannot have a variable, only a reference to it.

Consider the following C++ example :

SomeClass A(5);
SomeClass &B = A;
SomeClass &C = B;

Now, I think I’m right in saying that all of the three statements below will use the exact same object :

A.someMethod(); //some object
B.someMethod(); //the same object
C.someMethod(); //the same object

However, in Java, although objects are actually references, using the assignment operator will create an entirely new object with a new reference to it.

SomeClass A = new SomeClass();
SomeClass B;
B = A;

Now, the method calls will call from entirely different objects :

A.someMethod(); //uses one object
B.someMethod(); //uses entirely different object

Please tell me whether I am right or wrong.

Answer 1

References are different from objects. A particular object can have more than one reference pointing to it. When calling a method of a class at compile time always the class reference is checked whether the reference type contains the method defined in its class. If not a compile time error is issued. If the method is overridden in a subclass of the given class then the overridden method is called at run-time. At compile time always ‘class-ref’ in <class-ref>.method() is checked to see whether it contains the method definition. Other modifiers like static, final, abstract, method visibility are also checked at compile time itself and a compile time error is issued if the wrong combination of method modifiers is used.

    SomeClass A = new SomeClass();
    SomeClass B;
    B = A;        // Same class, same object, different reference


A.someMethod(); //uses one object
B.someMethod(); //uses the same object