CODEWITHSUNDEEP
java
Emiliyana Kalinova
Emiliyana Kalinova

Reputation: 55

Java constructors and super()

I have seen a few questions on the topic, but they all assume knowledge of inheritance. The example in my book is before the inheritance chapter, so the parent class is java.long.Object.

1. Scenario: my class FotoApparat has no custom constructor or any constructor at all and I create an instance of FotoApparat with FotoApparat meinFotoApparat = new FotoApparat()

Question: As my class has no constructor and also no super() call, I assume the program checks the parent Object class for a suitable constructor, which should be new Object(), right? If yes, is this still considered an "implicit" super() call?

2. Scenario: I create a custom constructor (by using eclipse source) which takes on parameters. In the generated constructor the super() call is added in the very beginning, which I assume is the actual implicit call I keep reading about. I read on javapoint that when an instance of a class is created, an instance of the parent class is also created, which is referenced by super().

Question: I read that this super() call can be removed from the constructor, but if it is removed and I use a constructor that takes on parameters, then (without super()) how is this parent object created ?!

Upvotes: 1

Views: 148

Answers (2)

Joni
Joni

Reputation: 111259

As my class has no constructor and also no space() call, I assume the program checks the parent Object class for a suitable constructor

Not quite. If you don't define a constructor, the compiler creates one for you. This constructor takes no arguments, and the only thing it does is call the super class constructor super().

when an instance of a class is created, an instance of the parent class is also created

Not quite: only one instance is created. There is no separate parent class instance.

The statement is not entirely incorrect because thanks to inheritance, the one instance of the child class that is created is also an instance of the parent class.

I read that this super() call can be removed from the constructor, but if it is removed and I use a constructor that takes on parameters, then (without super()) how is this parent object created ?!

In this scenario the compiler inserts a call to the no-argument super class constructor super(). But this does not create a separate "parent object" - only one object is created.

What your studies may not have made clear is the distinction between object creation and initialization. Calling a constructor does not "create" an object. An object is created by reserving space for it in memory. After the memory has been reserved, the constructor is called to "initialize" the object.

Upvotes: 1

Rick
Rick

Reputation: 1095

Scenario 1: If you don't define any constructor, a default, no-argument, constructor is created for you. That's the one that is called when using new FotoApparat(). This default constructor then calls the constructor on Object (see scenario 2.)

Scenario 2: If you don't explicitly call super(), this call is still done implicitly. It is possible however that the parent object does not have a constructor without arguments, in which case you are required to call a specific constructor.

Upvotes: 4

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