java - Does a superclass instance also being created when creating a subclass instance?

Question

I have seen many threads (e.g.: Inheritance in Java - creating an object of the subclass invokes also the constructor of the superclass. Why exactly?) saying that the instance of superclass will NOT be created when creating a subclass instance. I actually agree with this opinion.

However, I can't find any official materials (from Oracle) to back this up. I searched a couple of hours and cannot find anything. Can anyone refer me to a reliable resource to confirm this?

Answer 1

When you create a new instance and the class constructor is called, enough memory is being reserved in the heap for that instance's attributes to be stored. Those attributes comprise both:

• Attributes directly belonging to your class definition;
• Attributes belonging to all upper nodes in your class hierarchy tree.

Yes, the superclass constructor is called, but with the sole purpose to initialize attributes of the superclass. It never means a new object of the superclass will be created.

Check these links, they may help you to understand the process:

• http://www.javaworld.com/article/2076204/core-java/understanding-constructors.html
• http://docs.oracle.com/javase/tutorial/java/javaOO/objectcreation.html
• http://docs.oracle.com/javase/tutorial/java/javaOO/constructors.html

On the second link, documentation states: It is new which creates the object. That is: It reserves memory for all the class references (Object attributes) and primitive values. Then, the constructor is called, and its aim is to initialize enclosing class' attributes. Since the object attributes are references in Java, the constructor may use new to create object attributes, their references will be the values stored in your object's memory. The superclass constructor just continues this task for your class inherited attributes.