Functions as First Class Citizen Variables

Hello all, In this post we are going to talk about functions as first class citizens and it's usages.

taken from - https://www.linkedin.com/topic/functional-programming

The easiest way to understand is to analyze a demonstration. Package java.util.function  in java 8 contains all kinds of single method interfaces. In this samples we are going to use the java.util.function.Function and java.util.function.BiFunction interfaces.

1. Create  an inline lambda expression and store in a variable.

BiFunction<Integer, Integer, Integer> addFunction = (int1, int2) -> {
            return int1 + int2;
        };

to call the above method we can do as follows.

addFunction.apply(100, 200);

2. Create a static method that fits into the signature of the BiFunction interface, then assign it to the variable and invoke.

import java.util.function.BiFunction;

/**
 * Created by aruna on 2/7/17.
 */
public class Main {

    public static void main(String[] args) throws Exception {
        //create the variable
        BiFunction<Integer, Integer, Integer> addFunctionVariable;
        //assign the function to variable
        addFunctionVariable = Main::addStaticFunction;
        //invoke
        addFunctionVariable.apply(100, 200);
    }

    private static int addStaticFunction(int int1, int int2) {
        return int1 + int2;
    }
}

3. Create a instance method that fits to the signature of the BiFunction interface. In this approach, first we have to create the instance to acquire the function variable.

import java.util.function.BiFunction;

/**
 * Created by aruna on 2/7/17.
 */
public class Main {

    public static void main(String[] args) throws Exception {
        //create the variable
        BiFunction<Integer, Integer, Integer> addFunctionVariable;
        //create Main Object
        Main main = new Main();
        //assign the instance method to variable
        addFunctionVariable = main::addFunction;
        //invoke
        addFunctionVariable.apply(100, 200);
    }

    private int addFunction(int int1, int int2) {
        return int1 + int2;
    }
}

Now take an example, how to pass functions as variables and do some stuff.

import java.util.function.Function;

/**
 * Created by aruna on 2/7/17.
 */
public class Main {

    public static void main(String[] args) throws Exception {

        //define a function that multiply integer by 100
        Function<Integer, Integer> function = (intValue) -> { return intValue * 100;};
        //pass that function as a variable
        multiplyAndAdd(100 , 200, function);
    }
    private static int multiplyAndAdd(int int1, int int2, Function<Integer, Integer> function){

        if(function != null) {
            int1 = function.apply(int1);
            int2 = function.apply(int2);
        }

        return int1+ int2;
    }
}