Welcome!

Java IoT Authors: Harry Trott, Jenny Fong, Liz McMillan, Pat Romanski, Elizabeth White

Blog Feed Post

Losing Polymorphism with Java Lambda Expressions

Yesterday, I decided to re-write with lambdas one of the example I use while explaining polymorphism during my Java trainings. I realize that lambdas promote functional style of programming, while polymorphism is one of the crucial object-oriented features. Still, I decided to try mixing OOP and functional styles to see what happens.

The Task

The class Person has two descendants: Employee and Contractor. Also, there is an interface Payable that’s used to increase pay for workers.

public interface Payable {
   int INCREASE_CAP = 20;
   boolean increasePay(int percent);
}

Both Employee and Contract implement Payable, but the implementation of the increasePay() should be different. you can increase pay to the Employee by any percent, but the Contractor’s pay increase should stay under INCREASE_CAP.

The OOP version

Here’s the class Person:

public class Person {
	private String name;
	
	public Person(String name){
		this.name=name;
	}

	public String getName(){
		return "Person's name is " + name; 
	}
}

Here’s the Employee:

public class Employee extends Person  implements Payable{

   public Employee(String name){
     super(name);
    }
    public boolean increasePay(int percent) {
    System.out.println("Increasing salary by " + percent + "%. "+ getName()); 
    return true;
  }
}

Here’s the Contractor:

 public class Contractor extends Person implements Payable {
	
   public Contractor(String name){
 	super(name);
    }
   public boolean increasePay(int percent) {
	if(percent < Payable.INCREASE_CAP){
	  System.out.println("Increasing hourly rate by " + percent + 
                                      "%. "+ getName()); 
	  return true;
	} else {
	   System.out.println("Sorry, can't increase hourly rate by more than " + 
                       Payable.INCREASE_CAP + "%. "+ getName());
	   return false;
	}
  }
}

Here’s the code that will perform pay increase in a polymorphic way:

public class TestPayInceasePoly {

  public static void main(String[] args) {

     Payable workers[] = new Payable[3];
	workers[0] = new Employee("John");
	workers[1] = new Contractor("Mary");
	workers[2] = new Employee("Steve");		
	
        for (Payable p: workers){
	    p.increasePay(30);
	 }
  }
}

The output of this program looks like this:

Increasing salary by 30%. Person’s name is John
Sorry, can’t increase hourly rate by more than 20%. Person’s name is Mary
Increasing salary by 30%. Person’s name is Steve

Introducing Lambdas

Now I decided to experiment with lambdas. Namely, I wanted to pass a function as an argument to a method. I wanted to extract the increase pay logic from Employee and Contractor into lambda expressions and pass them to workers as argument to their methods.

I left the code of the Payable interface without any changes.

Here’s the new Person class that includes the method validatePayIncrease, which will take a lambda expression as a first argument (passing a function to a method):

public class Person {
	
	private String name;

	public Person (String name){
		this.name = name;
	}
	
	public String getName(){
		return name;
	}
	
	public boolean validatePayIncrease(Payable increaseFunction, int percent) {
			 
         boolean isIncreaseValid= increaseFunction.increasePay(percent); 
         	 
         System.out.println( " Increasing pay for " + name + " is " + 
        	              (isIncreaseValid? "valid.": "not valid."));
		 return isIncreaseValid;
	}
}

The new version of Employee doesn’t implements Payable:

public class Employee extends Person{

  // some other code specific to Employee goes here

  public Employee(String name){
	  super(name);
  } 
}

The new version of Contractor doesn’t implements Payable either:

	  
public class Contractor extends Person{
    

  // some other code specific to Contractor goes here

    public Contractor(String name){
       super(name);
    }
}

Finally, the program that will increase the pay to all workers passing different lambda expressions to employees and contractors.

public class TestPayIncreaseLambda {
	
  public static void main(String[] args) {

        Person workers[] = new Person[3];
		workers[0] = new Employee("John");
		workers[1] = new Contractor("Mary");
		workers[2] = new Employee("Steve");		

	  // Lambda expression for increasing Employee's pay
	   Payable increaseRulesEmployee = (int percent) -> {
				return true;
	   };
	   
		// Lambda expression for increasing Contractor's pay	   
	    Payable increaseRulesContractor = (int percent) -> {
	    	if(percent > Payable.INCREASE_CAP){
	    		System.out.print(" Sorry, can't increase hourly rate by more than " + 
	    	             Payable.INCREASE_CAP + "%. "); 
				return false;
			} else {	
				return true;
			}
	   };	
	   
	   for (Person p: workers){
		   if (p instanceof Employee){
			   // Validate 30% increase for every worker
			   p.validatePayIncrease(increaseRulesEmployee, 30); 
		   } else if (p instanceof Contractor){
			   p.validatePayIncrease(increaseRulesContractor, 30);
		   }
	   }
  }

}

As you see, I’m passing one or the other lambda expression to the method validatePayIncrease. Running this program produces the following output:

Increasing pay for John is valid.
Sorry, can’t increase hourly rate by more than 20%.  Increasing pay for Mary is not valid.
Increasing pay for Steve is valid.

It works, but so far I like my OOP version better than the lambda’s one:

1. In the OOP version I’ve enforced a contract – both Employee and Contractor must implement Payable. In the lambda’s version it’s gone on the class level. On the plus side, the strong typing still exists in the lambda’s version –  the type of the valiastePayIncrease first argument is Payable.

2. In the OOP version I didn’t use type checking, but in the lambda’s version this ugly instanceof creeped in.

While it’s cool that I can pass the function to the object and execute it there, the price seems to be high. Let’s see if this code can be further improved.

Getting rid of the class hierarchy

Currently the code in Employee and Contractor is the same. If the only difference in their code is implementation of the validatePayIncrease method, we can remove the inheritance hierarchy and just add the property boolean workerStatus to the class Person to distinguish employees from contractors.

Let’s get rid of the classes Employee and Contractor and modify the Person. I’ll add the second argument to the constructor workerStatus.

public class Person {
	
	private String name;
	private char workerStatus;  // 'E' or 'C'

	public Person (String name, char workerStatus){
		this.name = name;
		this.workerStatus=workerStatus;
	}
	
	public String getName(){
		return name;
	}
	
	public char getWorkerStatus(){
		return workerStatus;
	}
	
	public boolean validatePayIncrease(Payable increaseFunction, int percent) {
			 
         boolean isIncreaseValid= increaseFunction.increasePay(percent); 
         	 
         System.out.println( " Increasing pay for " + name + " is " + 
        	              (isIncreaseValid? "valid.": "not valid."));
		 return isIncreaseValid;
	}
}

The code of the TestPayIncreaseLambda will become simpler now. We don’t need to store objects of different types in the array workers and can get rid of the instanceof:

public class TestPayIncreaseLambda {
	
  public static void main(String[] args) {

        Person workers[] = new Person[3];
		workers[0] = new Person("John", 'E');
		workers[1] = new Person("Mary", 'C');
		workers[2] = new Person("Steve", 'E');		

	  // Lambda expression for increasing Employee's pay
	   Payable increaseRulesEmployee = (int percent) -> {
				return true;
	   };
	   
		// Lambda expression for increasing Contractor's pay	   
	    Payable increaseRulesContractor = (int percent) -> {
	    	if(percent > Payable.INCREASE_CAP){
	    		System.out.print(" Sorry, can't increase hourly rate by more than " + 
	    	             Payable.INCREASE_CAP + "%. "); 
				return false;
			} else {	
				return true;
			}
	   };	
	   
	   for (Person p: workers){
		   if ('E'==p.getWorkerStatus()){
			   // Validate 30% increase for every worker
			   p.validatePayIncrease(increaseRulesEmployee, 30); 
		   } else if ('C'==p.getWorkerStatus()){
			   p.validatePayIncrease(increaseRulesContractor, 30);
		   }
	   }
  }
}

The purists may not like the fact that I’m using hardcoded ‘E’ and ‘C’.You can add a couple of final variables EMPLOYEE and CONTRACTOR at the top of this class.
So what’s the verdict? Losing polymorphism may not be a bad thing, or is it?


Read the original blog entry...

More Stories By Yakov Fain

Yakov Fain is a Java Champion and a co-founder of the IT consultancy Farata Systems and the product company SuranceBay. He wrote a thousand blogs (http://yakovfain.com) and several books about software development. Yakov authored and co-authored such books as "Angular 2 Development with TypeScript", "Java 24-Hour Trainer", and "Enterprise Web Development". His Twitter tag is @yfain

@ThingsExpo Stories
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 19th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world and ThingsExpo Silicon Valley Call for Papers is now open.
Machine Learning helps make complex systems more efficient. By applying advanced Machine Learning techniques such as Cognitive Fingerprinting, wind project operators can utilize these tools to learn from collected data, detect regular patterns, and optimize their own operations. In his session at 18th Cloud Expo, Stuart Gillen, Director of Business Development at SparkCognition, discussed how research has demonstrated the value of Machine Learning in delivering next generation analytics to imp...
SYS-CON Events announced today that ReadyTalk, a leading provider of online conferencing and webinar services, has been named Vendor Presentation Sponsor at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. ReadyTalk delivers audio and web conferencing services that inspire collaboration and enable the Future of Work for today’s increasingly digital and mobile workforce. By combining intuitive, innovative tec...
Amazon has gradually rolled out parts of its IoT offerings, but these are just the tip of the iceberg. In addition to optimizing their backend AWS offerings, Amazon is laying the ground work to be a major force in IoT - especially in the connected home and office. In his session at @ThingsExpo, Chris Kocher, founder and managing director of Grey Heron, explained how Amazon is extending its reach to become a major force in IoT by building on its dominant cloud IoT platform, its Dash Button strat...
Connected devices and the industrial internet are growing exponentially every year with Cisco expecting 50 billion devices to be in operation by 2020. In this period of growth, location-based insights are becoming invaluable to many businesses as they adopt new connected technologies. Knowing when and where these devices connect from is critical for a number of scenarios in supply chain management, disaster management, emergency response, M2M, location marketing and more. In his session at @Th...
The cloud market growth today is largely in public clouds. While there is a lot of spend in IT departments in virtualization, these aren’t yet translating into a true “cloud” experience within the enterprise. What is stopping the growth of the “private cloud” market? In his general session at 18th Cloud Expo, Nara Rajagopalan, CEO of Accelerite, explored the challenges in deploying, managing, and getting adoption for a private cloud within an enterprise. What are the key differences between wh...
It is one thing to build single industrial IoT applications, but what will it take to build the Smart Cities and truly society changing applications of the future? The technology won’t be the problem, it will be the number of parties that need to work together and be aligned in their motivation to succeed. In his Day 2 Keynote at @ThingsExpo, Henrik Kenani Dahlgren, Portfolio Marketing Manager at Ericsson, discussed how to plan to cooperate, partner, and form lasting all-star teams to change t...
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life sett...
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...
There are several IoTs: the Industrial Internet, Consumer Wearables, Wearables and Healthcare, Supply Chains, and the movement toward Smart Grids, Cities, Regions, and Nations. There are competing communications standards every step of the way, a bewildering array of sensors and devices, and an entire world of competing data analytics platforms. To some this appears to be chaos. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, Bradley Holt, Developer Advocate a...
SYS-CON Events announced today that Bsquare has been named “Silver Sponsor” of SYS-CON's @ThingsExpo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. For more than two decades, Bsquare has helped its customers extract business value from a broad array of physical assets by making them intelligent, connecting them, and using the data they generate to optimize business processes.
There is little doubt that Big Data solutions will have an increasing role in the Enterprise IT mainstream over time. Big Data at Cloud Expo - to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA - has announced its Call for Papers is open. Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is...
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, wh...
Cognitive Computing is becoming the foundation for a new generation of solutions that have the potential to transform business. Unlike traditional approaches to building solutions, a cognitive computing approach allows the data to help determine the way applications are designed. This contrasts with conventional software development that begins with defining logic based on the current way a business operates. In her session at 18th Cloud Expo, Judith S. Hurwitz, President and CEO of Hurwitz & ...
Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is expected in the amount of information being processed, managed, analyzed, and acted upon by enterprise IT. This amazing is not part of some distant future - it is happening today. One report shows a 650% increase in enterprise data by 2020. Other estimates are even higher....
In his general session at 18th Cloud Expo, Lee Atchison, Principal Cloud Architect and Advocate at New Relic, discussed cloud as a ‘better data center’ and how it adds new capacity (faster) and improves application availability (redundancy). The cloud is a ‘Dynamic Tool for Dynamic Apps’ and resource allocation is an integral part of your application architecture, so use only the resources you need and allocate /de-allocate resources on the fly.
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportuni...
industrial company for a multi-year contract initially valued at over $4.0 million. In addition to DataV software, Bsquare will also provide comprehensive systems integration, support and maintenance services. DataV leverages advanced data analytics, predictive reasoning, data-driven diagnostics, and automated orchestration of remediation actions in order to improve asset uptime while reducing service and warranty costs.
Vidyo, Inc., has joined the Alliance for Open Media. The Alliance for Open Media is a non-profit organization working to define and develop media technologies that address the need for an open standard for video compression and delivery over the web. As a member of the Alliance, Vidyo will collaborate with industry leaders in pursuit of an open and royalty-free AOMedia Video codec, AV1. Vidyo’s contributions to the organization will bring to bear its long history of expertise in codec technolo...