Static Factory Methods

Consider using Static Factory Methods Instead of Constructors

The static factory method is a method that returns an instance of the class.

Example

In this example, we will build some HTML elements using Java. Here is the base class.

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class HtmlElement {
    private final String tag;
    private final String content;

    public HtmlElement(String tag, String content) {
        this.tag = tag;
        this.content = content;
    }

    @Override
    public String toString() {
        return "<" + tag + "> " + content + " </" + tag + ">";
    }
}

Instead of providing a normal constructor, we can provide the of static factory method:

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class Div extends HtmlElement {
    private Div(String tag, String content) {
        super(tag, content);
    }

    public static Div of(String content) {
        return new Div("div", content);
    }
}

So that, we can create new divs using this method:

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class Demo {
    public static void main(String[] args) {
        final Div div1 = Div.of("Hello, World!");
        final Div div2 = Div.of("Hi, People!");

        System.out.println(div1);
        System.out.println(div2);
    }
}

Here is the output of the demo above:

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<div> Hello, World! </div>
<div> Hi, People! </div>

Why?

  • Static Factory Methods have names - easier to know and use especially if we have multiple static factory methods VS multiple overridden constructors!
  • Static Factory Methods do not require creating a new object each time - you may use some cache or a singleton behavior.
  • Static Factory Methods can return an object with a type of sub-class if needed! The constructors cannot.

Why Not?

  • Classes with only Static Factory Methods can not be subclassed - unless you added at least one protected or public constructor, you may need to add multiple constructors as well.
  • Constructors are easier to be found and highlighted by the IDEs for developers.

Common Names

There are multiple common names for Static Factory Methods, some of them are: of, from, create, getInstance, and valueOf.

Read more about this topic from our resource below.

Resources