Anonymous recursion in Java

Factorial.java

import java.util.function.Function;
import java.util.function.UnaryOperator;

class Factorial {
    static <T, R> Function<T, R> fix(UnaryOperator<Function<T, R>> operator) {
        return operator.apply(argument -> fix(operator).apply(argument));
    }
    
    static Function<Integer, Integer> factorial = fix(f -> n -> n == 0 ? 1 : n * f.apply(n - 1));
}