Editing Function object (section)

== In Java ==
[[Java (programming language)|Java]] has no [[first-class function]]s, so function objects are usually expressed by an interface with a single method (most commonly the <code>Callable</code> interface), typically with the implementation being an anonymous [[inner class]], or, starting in Java 8, a [[anonymous function|lambda]].

For an example from Java's standard library, <code>java.util.Collections.sort()</code> takes a <code>List</code> and a functor whose role is to compare objects in the List. Without first-class functions, the function is part of the Comparator interface. This could be used as follows.

<syntaxhighlight lang="java">
List<String> list = Arrays.asList("10", "1", "20", "11", "21", "12");

Comparator<String> numStringComparator = new Comparator<String>() {
    public int compare(String str1, String str2) {
        return Integer.valueOf(str1).compareTo(Integer.valueOf(str2));
    }
};

Collections.sort(list, numStringComparator);
</syntaxhighlight>

In Java 8+, this can be written as:
<syntaxhighlight lang="java">
List<String> list = Arrays.asList("10", "1", "20", "11", "21", "12");

Comparator<String> numStringComparator = (str1, str2) -> Integer.valueOf(str1).compareTo(Integer.valueOf(str2));

Collections.sort(list, numStringComparator);
</syntaxhighlight>