Concepts in Lamda programming

Usage of Function, Method Reference and Closure in functional programming

package com.java8.chapter3;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.function.Function;

import java.util.function.ToIntFunction;

/* Example of Function<R,T> interface i.e. Converting an object from one DT to another DT

 * Use of Closure in lamda and anonymous inner class

 * Use of Method Reference, replacement of lamda

 * R apply(T t);

*/

public class FunctionLamda {

     public static void main(String[] args) {

List<Integer> list = Arrays.asList(2, 4, 6, 8);

          

// Printing list<Integer>

list.stream().forEach(p -> System.out.println(p));

          

// perform any operation on each element of list and print

System.out.println(performOperation(list,p->p*2));

          

// Create new Integer list(length of String) from list of Strings using  Function<String,Integer>

System.out.println(extractOperation(Arrays.asList("Paras","Suriender","Sham"), s->s.length()));

          

// Create new Integer list(length of String) from list of Strings using ToIntFunction<String>

System.out.println(extractOperation2(Arrays.asList("Paras","Suriender","Sham"), s->s.length()));

    

/* Lamda and annonymous function accessing variables outside of local space

* Closure -a closure is an instance of a function that can reference nonlocal variables of that

function with no restrictions

*/

          

int a=10,b=20;

Thread thread1 = new Thread(new Runnable() {

           public void run() {

           System.out.println(a+b);

     }

     });

thread1.start();

          

Thread thread = new Thread(()-> System.out.println(a));

thread.start();

          

          

Function<String, Integer> stringToInteger =(String s) -> Integer.parseInt(s);

System.out.println(stringToInteger.apply("12346"));

          

// Method Reference , Class :: static method

Function<String, Integer> stringToInteger2 =Integer::parseInt;

System.out.println(stringToInteger2.apply("4123"));

          

}

     public static List<Integer> performOperation(List<Integer> list, Function<Integer, Integer> function) {

           List<Integer> result = new ArrayList<Integer>();

           for(Integer p : list){

                result.add(function.apply(p));

           }

           return result;

     }

     public static List<Integer> extractOperation(List<String> list, Function<String, Integer> function) {

           List<Integer> result = new ArrayList<Integer>();

           for(String p : list){

                result.add(function.apply(p));

           }

           return result;

     }

     public static List<Integer> extractOperation2(List<String> list, ToIntFunction<String> function) {

           List<Integer> result = new ArrayList<Integer>();

           for(String p : list){

                result.add(function.applyAsInt(p));

           }

           return result;

     }

}

Output:

2 4 6 8

[4, 8, 12, 16]

[5, 9, 4]

[5, 9, 4]

30

10

12346

4123