When do you need to explicitly call a superclass constructor?

java constructor subclass superclass
jhlu87 picture jhlu87 · Jun 11, 2011 · Viewed 59.4k times · Source

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?

I'm looking at an example in a book about abstract classes and when they extend it with a non-abstract subclass, the subclass's default constructor is blank and there's a comment that says the superclass's default constructor will be called. At the same time I've also seen instances on here where someone's problem was not explicitly calling super().

Is the distinction from calling the superclass's default/non-default constructor from the subclass's default/non-default constructor?

Answer

Jon Skeet picture Jon Skeet · Jun 11, 2011

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...

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