When do you need to explicitly call a superclass constructor?

Question

So say I have a subclass that extends a superclass. In what scenarios do I need to explicitly type super() to get the superclass constructor to run?

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Answer 1

You never need just

super();

That's what will be there if you don't specify anything else. You only need to specify the constructor to call if:

• You want to call a superclass constructor which has parameters
• You want to chain to another constructor in the same class instead of the superclass constructor

You claim that:

At the same time I've also seen instances on here where someone's problem was not explicitly calling super().

Could you give any examples? I can't imagine how that's possible...

Answer 2

If you don't explicitly call a super constructor the argument less constructor (super()) will be called. This means you have to call a specific constructor yourself if there's no reachable argument-less constructor of the super class.

But often enough you want a different constructor anyways even if you could use the default constructor - depends on your code.

Also note that if no constructor is declared the compiler generates a public default constructor automatically, but as soon as you write your own constructor this does not happen anymore.

Answer 3

The super() method is always called in constructors of sub-classes, even if it is not explicitly written in code.

The only time you need to write it, is if there are several super(...) methods in the super-class with different initialization parameters.