Which of these classes has a default constructor?

Question

Which of these classes has a default constructor? I'm thinking just A but am I wrong?

class A {}
class B {B() {}}
class C {C(int j) {}}

Possible duplicate of [Java default constructor](http://stackoverflow.com/questions/4488716/java-default-constructor) — MWiesner, Feb 03 '16 at 19:07

tnw · Answer 1 · 2016-02-03T19:07:41.743

2

You are correct. A default constructor is, by definition, created when no constructor is defined. Since A does not have a constructor defined it will have a default constructor created for it.

Technically speaking, you could say B has a default constructor since a parameter-less constructor is what would be created if none is defined.

Reference: http://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#jls-8.8.9

edited Feb 03 '16 at 19:07

answered Feb 03 '16 at 18:27

tnw

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Could you please add a reference to the "definition", might be helpful. – MWiesner Feb 03 '16 at 18:28
Added the closest thing I could find in the java documentation. – tnw Feb 03 '16 at 18:30
please update your reference to point to the official language specification instead of a tutorial: http://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#jls-8.8.9 – MWiesner Feb 03 '16 at 18:36
1

@MWiesner Updated. Thanks for digging that up! – tnw Feb 03 '16 at 19:08

score 0 · Answer 2 · edited Feb 03 '16 at 18:48

Precisely.

Class A has a default constructor because you're not providing any constructor for the class. The compiler, therefore, automatically provides a no-argument, default constructor. This default constructor will call the no-argument constructor of the superclass (in this case the Object class). The second class, Class B, is providing a no-argument constructor, but it is not default as the compiler is not providing it for you.

Which of these classes has a default constructor?

2 Answers2