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Data Mining. Connect and share knowledge within a single location that is structured and easy to search. Which of the below classes will use a default constructor, when we initialize an object from them? But what about Y? Or should there be no constructor defined in the class when we can speak of a default constructor when initializing an object? If you have define a empty argument constructor to a Class, then user defined empty argument constructor will replace default constructor which generated by compiler.
The default constructor is the no-argument constructor automatically generated unless you define another constructor with no argument.
Check JLS 8. Default constructor mean, Compiler generated, no argument constructor. Every other Constructors are called used defined constructors. A constructor is always called when constructing a new object, and a constructor of every superclass of the class is also called. If no constructor is explicitly called, the default constructor is called which may or may not be declared. DefaultConstructor JLS. The default constructor is the one Java provides by default.
And since I don't want it - as it's useless, I might feel inclined to put skull and crossbones on it:. But I still can't forbid another developer to create a method inside the Person class, so marking the constructor as private didn't help :.
All this fuss could be - and is - avoided thanks to the fact that Java and not only Java works the way it works. If you define a method setCoordinates int x, int y , you don't expect compiler to automatically accept a parameterless version of it - setCoordinates. It wouldn't do a thing.
How is this different from expecting a parameterless constructor? Well, obviously, a constructor always does at least one thing - it creates an object or dies trying. But I like to be in control of how I want my objects to be instantiated. Forcing me to have a parameterless constructor no matter what I do takes this control away from me. The language puts the default constructor in as a favor to you.
The presumption is that if you've written a custom constructor, your no-argument constructor may well require special attention too. Not a great reason, but not horrible, either. The secondary reason id that cruft just gets pile onto that language with no thought to its symmetry with existing practice and very little interest in making it readable.
Stoustroup's original "C with Classes" was a hacked up C-preprocessor which probably shouldn't made it out of the lab. The world's funny that way. If you define a constructor with a parameter, then there must be a valid reason in doing so. Maybe this parameter is so important to your class that without it the object state is invalid. That is why the Java does not make a no-argument constructor for you when you already define one.
Sign up to join this community. The best answers are voted up and rise to the top. Exception Handling in Java. Collection Framework. Multi-threading in Java. Table of Contents. Save Article. Improve Article. Like Article. String name;. Geek String name, int id. Geek String name. Geek String name, int age. Geek long id. Output Constructor with one argument - String : Shikhar Constructor with two arguments : String and Integer : Dharmesh 26 Constructor with one argument : Long : Previous Need of Wrapper Classes in Java.
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