Does a Java constructor return the Object reference?

Question

I know Java's constructors can't have any type and interestingly it cannot even be void . A logical explanation for that would be that a constructor returns the initialized object's reference.

MyClass myObject = new MyClass();

The constructor of myClass will now return the object reference after instantiating it and save it in the object variable MyObject and that's why the constructor can't have a return type.

Is that right? Could someone confirm this?

Answer 1

No, actually, the constructors are compiled into the class file like methods having the name <init> and a void return type. You can see these "<init>" invocations in stack traces. The expression new Type() is compiled as an instruction new which just creates the instance of Type and an additional method invokation ( invokespecial ) to one of the constructors declared in Type .

The verifier will ensure that such a special method is invoked at exactly once on a newly created instance and that it is called before any other use of the object.

It's just a programming language design decision to let constructors have no return type from the Java language point of view. After all, new Type(…) is an expression that evaluates to the newly created instance of Type and you can't get a return value from the constructor with that programming language construct. Further, if you add a return type, Java will unconditionally assume that it is a method, even if it has the same name as the class.

That's simply how it was defined : (It makes parsing the class definition easier)

The SimpleTypeName in the ConstructorDeclarator must be the simple name of the class that contains the constructor declaration, or a compile-time error occurs.

In all other respects, a constructor declaration looks just like a method declaration that has no result (§8.4.5).

Answer 2

I suppose you could say that constructors have a "special syntax" used specifically for returning instances of the desired object. You do not specify the return type in these cases. The new keyword is used together with the constructor method to produce an instance of the class type.

If you'd like to control the return type of an instance generation method, then you should probably be looking at using a type of factory design pattern, wherein a static method creates an instance (using a constructor), and then returns a more explicit type (say for example, the super type, or an interface type).

This pattern is good when you'd like to decide which type to return based on some parameter, but leave the actual type hidden to the consumer of the instance generation method.

Answer 3

A constructor is not a methed. It does not return anything. It is used for initialization purposes, especially useful when those initializations depend on parameters or there is a chance that exceptions will be thrown (though both are optional).

So, unlike a method, it is not inherited and does not have a return type (not even void).

Answer 4

The idea is that you are "constructing" an instance of MyClass by calling the constructor itself. The idea of the constructor is to instantiate and not to return. Having created myObject you can then refer to public methods and variables part of its declaration which will provide you with the required data being returned as an answer to a call. It is important to understand that the constructor does not return anything it simply creates an instance which can then be used to refer to methods and variables (which return data) declared within the instantiated class.