Defining functions in Java

SampleFunction.java

import java.util.function.Function;

import static java.lang.String.format;

class Scratch {
    public static void main(String[] args) {
        //instantiate as an object
        Function<Integer, String> stringifyInteger = stringifyInteger();
        System.out.println(format("Output is %s", stringifyInteger.apply(3)));

        //lambda format
        Function<Integer, String> stringifyIntegerLambda = a -> a.toString();
        System.out.println(format("Output is %s", stringifyIntegerLambda.apply(3)));

        //method reference
        Function<Integer, String> stringifyIntegerMethodRef = Object::toString;
        System.out.println(format("Output is %s", stringifyIntegerMethodRef.apply(3)));

    }

    private static Function<Integer, String> stringifyInteger(){
        return new Function<Integer, String>() {
            @Override
            public String apply(Integer integer) {
                return integer.toString();
            }
        };
    }
}