Constructor overloading in Java - best practice

user_114626 0
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There are a few topics similar to this, but I couldn't find one with a sufficient answer.

I would like to know what is the best practice for constructor overloading in Java. I already have my own thoughts on the subject, but I'd like to hear more advice.

I'm referring to both constructor overloading in a simple class and constructor overloading while inheriting an already overloaded class (meaning the base class has overloaded constructors).

Thanks :)

constructor-overloading overloading constructor java
5 Answers

I think the best practice is to have single primary constructor to which the overloaded constructors refer to by calling this() with the relevant parameter defaults. The reason for this is that it makes it much clearer what is the constructed state of the object is - really you can think of the primary constructor as the only real constructor, the others just delegate to it

One example of this might be JTable - the primary constructor takes a TableModel (plus column and selection models) and the other constructors call this primary constructor.

For subclasses where the superclass already has overloaded constructors, I would tend to assume that it is reasonable to treat any of the parent class's constructors as primary and think it is perfectly legitimate not to have a single primary constructor. For example,when extending Exception, I often provide 3 constructors, one taking just a String message, one taking a Throwable cause and the other taking both. Each of these constructors calls super directly.

user_168530

If you have a very complex class with a lot of options of which only some combinations are valid, consider using a Builder. Works very well both codewise but also logically.

The Builder is a nested class with methods only designed to set fields, and then the ComplexClass constructor only takes such a Builder as an argument.

Edit: The ComplexClass constructor can ensure that the state in the Builder is valid. This is very hard to do if you just use setters on ComplexClass.

user_538970

It really depends on the kind of classes as not all classes are created equal.

As general guideline I would suggest 2 options:

  • For value & immutable classes (Exception, Integer, DTOs and such) use single primary constructor as suggested in above answer
  • For everything else (session beans, services, mutable objects, JPA & JAXB entities and so on) use default constructor only with sensible defaults on all the properties so it can be used without additional configuration
user_1385610

Constructor overloading is like method overloading. Constructors can be overloaded to create objects in different ways.

The compiler differentiates constructors based on how many arguments are present in the constructor and other parameters like the order in which the arguments are passed.

For further details about java constructor, please visit https://tecloger.com/constructor-in-java/

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