Nullary constructor

<h2 id="object-oriented-constructors">Object-oriented constructors</h2>
<p>In <a href="/facts/Object-oriented_programming/TxNMEcao">object-oriented programming</a>, a <a href="/facts/Constructor_(computer_science)/8JNHsH5H">constructor</a> is code that is run when an <a href="/facts/Object_(computer_science)/eX99dtAw">object</a> is created. <a href="/facts/Default_constructor/UnyxDE4K">Default constructors</a> of objects are usually nullary.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
<h3>Java example</h3>
public class Example 
{
    protected int data;

/* Nullary constructor */
    public Example()
    {
        this(0);
    }

/* Non-nullary constructor */
    public Example(final int data)
    {
        this.data = data;
    }
}

<h2 id="algebraic-data-types">Algebraic data types</h2>
<p>In <a href="/facts/Algebraic_data_types/Fn9KhnAb">algebraic data types</a>, a constructor is one of many tags that wrap data. If a constructor does not take any data arguments, it is nullary.
</p>
<h3>Haskell example</h3>
-- nullary type constructor with two nullary data constructors
data Bool = False
          | True

-- non-nullary type constructor with one non-nullary data constructor
data Point a = Point a a

-- non-nullary type constructor with...
data Maybe a = Nothing -- ...nullary data constructor
             | Just a  -- ...unary data constructor

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Default Constructor in Java – Class Constructor Example". freeCodeCamp.org. 2022-01-13. Retrieved 2022-03-23. <a href="https://www.freecodecamp.org/news/default-constructor-in-java/" target="_blank">https://www.freecodecamp.org/news/default-constructor-in-java/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"No-argument Constructor". chortle.ccsu.edu. Retrieved 2022-03-23. <a href="https://chortle.ccsu.edu/java5/Notes/chap50/ch50_13.html" target="_blank">https://chortle.ccsu.edu/java5/Notes/chap50/ch50_13.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"Default constructors - cppreference.com". en.cppreference.com. Retrieved 2023-04-12. <a href="https://en.cppreference.com/w/cpp/language/default_constructor" target="_blank">https://en.cppreference.com/w/cpp/language/default_constructor</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Ottinger, Joseph B.; Linwood, Jeff; Minter, Dave (2022), Ottinger, Joseph B.; Linwood, Jeff; Minter, Dave (eds.), "An Introduction to Hibernate 6", Beginning Hibernate 6: Java Persistence from Beginner to Pro, Berkeley, CA: Apress, pp. 1–25, doi:10.1007/978-1-4842-7337-1_1, ISBN 978-1-4842-7337-1, retrieved 2022-03-23 <a href="978-1-4842-7337-1" target="_blank">978-1-4842-7337-1</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
</ol>

Nullary constructor open-in-new

Nullary constructor