Java 8 Features | stream processing and lambda expressions

There are lots of programming languages in the world today, and some of them are quiet popular. Each language has their own features, syntax and rules. There is one method of programming called functional programming, where you declare what do you need rather then how do you do it. Lots of languages has these features, for example python, bash, c#. In spite of being one of the most popular languages, java has been behind in putting stream processing and lambda expressions into itself for almost four years and finally it did it.

Below are some of the code examples of stream processing and lambda expressions combined that, if you were unfamiliar with it, you will be blown away.

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.function.BiFunction;
import java.util.stream.Collectors;

public class BiFunctionExample {

 public static void main(String[] args) {
  biFunctionStringConcat();
  biFunctionExample();
  byFunctionFilterExample();
 }
 public static void byFunctionFilterExample(){
  List<Double> lst = new ArrayList<Double>();
  lst.add(2d);
  lst.add(200d);
  lst.add(6d);
  lst.add(60d);
  lst.add(122d);
  lst.add(876d);
  lst.add(738d);
  lst.add(333d);
  lst.add(112d);
  lst.add(98d);
  lst.add(0d);
  lst.add(3d);
  lst.add(1d);
  lst.add(6666d);
  
  List<Double> resultList = lst.stream()
   .sorted()
   .filter( x -> x > 20d )
   .collect(Collectors.toList());
  
  Double sumResultList = resultList.stream().reduce(0d,  Double::sum);
  Double max = resultList.stream().max(Comparator.comparing(x -> x)).get();
  String plusItems = resultList.stream()
    .map(x -> x.toString())
    .reduce((x, y) -> x + " + " + y)
    .get();
  
  System.out.println(resultList);
  System.out.println(plusItems);
  System.out.println("Sum = " + sumResultList);
  System.out.println("max = " + max);
 }

 public static void biFunctionExample() {
  BiFunction<Double, Double, List<Double>> bi = (x,y) -> {
   List<Double> list = new ArrayList<Double>();
   list.add(Math.pow(x, y));
   list.add(x * y);
   return list;
  };
  
  System.out.println(bi.apply(2d, 3d));
 }
 
 public static void biFunctionStringConcat(){
  BiFunction<String, String,String> bi = (x, y) -> {      
        return x + y;
      };

      System.out.println(bi.apply("rajan", " upadhyay"));
 }
}

Enjoy!!

Creating a simple Class Diagram

Question

Write a program that calculates the cost to send packages within the US. There are 3

different ways to send a package:

Multiple Inheritance in java

Its obvious that there are lot of problems related to ambiguity in multiple inheritance. While C++ found a solution to the problem, java decided not to go with multiple inheritance. Instead, they have a different way of doing it. Before implementing multiple inheritance equivalent in Java, you need to be familiar with a few terms.

Inheritance : It is the case when a child class extends a parent class. This is a "is a" relation.

Association: It is the situation where a class may have one or more objects of another class. There is a "has a" relationship between one object to another. The association may be strong when deleting the main objects automatically deletes the other objects as well. While if the other objects still have some value without the main object, such association is called weak association.