Click here to close now.


Java IoT Authors: Anders Wallgren, Liz McMillan, Greg O'Connor, Dana Gardner, Steve Watts

Related Topics: Java IoT, Microservices Expo

Java IoT: Book Excerpt

How to Get Started with Java and NetBeans

Book Excerpt: Essential Java Skills (Part 1)

When Sun's developers created Java, they tried to keep the syntax for Java similar to the syntax for C++ so it would be easy for C++ programmers to learn Java. In addition, they designed Java so its applications can be run on any computer platform. In contrast, C++ needs to have a specific compiler for each platform. Java was also designed to automatically handle many operations involving the creation and destruction of memory. This is a key reason why it's easier to develop programs and write bug-free code with Java than with C++. To provide these features, the developers of Java had to sacrifice some speed (or performance) when compared to C++. For many types of applications, however, Java's relative slowness is not an issue.

Microsoft's Visual C# language is similar to Java in many ways. Like Java, C# uses a syntax that's similar to C++ and that automatically handles memory operations. However, in practice, C# code only runs on Windows. Because of that, C# is a good choice for developing applications for a Windows-only environment. However, Java is a better choice if you need to develop crossplatform applications.

Applications, Applets, and Servlets
Figure 1 describes the three types of programs that you can create with Java. First, you can use Java to create applications that run directly on your computer. These are also known as desktop applications.

When you create these desktop applications, you can use a graphical user interface (GUI) to get user input and perform a calculation as shown at the top left of this figure. In chapter 15, you'll learn how to create these types of applications. Until then, you'll learn how to create another type of desktop application known as a console application. This type of application runs in the console, or command prompt, that's available from your operating system. An example of a console application is shown at the top right of this figure.

One of the unique characteristics of Java is that you can use it to create a special type of web-based application known as an applet. For instance, this figure shows an applet that works the same way as the applications above it. The main difference between an application and an applet is that an applet can be stored in an HTML page and can run inside a Java-enabled browser. As a result, you can distribute applets via the Internet or an intranet. In chapter 17, you'll learn how to create and deploy applets.

Although applets can be useful for creating a complex user interface within a browser, they have their limitations. First, you usually need to install a plug-in on each client machine, which isn't ideal for some types of applications. Second, since an applet runs within a browser on the client, it's not ideal for working with resources that run on the server, such as enterprise databases.

To provide access to enterprise databases, many developers use Java EE to create applications that are based on servlets. A servlet is a special type of Java application that runs on the server and can be called by a client, which is usually a web browser. This is also illustrated in this figure. Here, you can see that the servlet works much the same way as the applet. The main difference is that the code for the application runs on the server.

When a web browser calls a servlet, the servlet performs its task and returns the result to the browser, typically in the form of an HTML page. For example, suppose a browser requests a servlet that displays all unprocessed invoices that are stored in a database. Then, when the servlet is executed, it reads data from the database, formats that data within an HTML page, and returns the HTML page to the browser.

When you create a servlet-based application like the one shown here, all the processing takes place on the server and only HTML is returned to the browser. That means that anyone with an Internet or intranet connection, a web browser, and adequate security clearance can access and run a servlet-based application. Because of that, you don't need to install any special software on the client. To make it easy to store the results of a servlet within an HTML page, the Java EE specification provides for JavaServer Pages (JSPs). Most developers use JSPs together with servlets when developing server-side Java applications.

Although servlets and JSPs aren't presented in this book, we cover this topic in a companion book, Murach's Java Servlets and JSP. For more information about this book, please visit our web site at

A GUI application and a console application

An applet

A servlet

Figure 1: Applications, applets, and servlets

The Code for the Console Version of the Future Value Application
To give you an idea of how the code for a Java application works, Figure 2 presents the code for the console version of the Future Value application that you saw in figure 1-2.

If you have experience with other programming languages, you may be able to understand much of this code already. If not, don't worry! You'll learn how all of this code works in the next few chapters. For now, here's a brief explanation of this code.

Most of the code for this application is stored in a class named FutureValueApp. This class begins with an opening brace ({) and ends with a closing brace (}). Within this class, two methods are defined. These methods also begin with an opening brace and end with a closing brace, and they are indented to clearly show that they are contained within the class.

The first method, named main, is the main method for the application. The code within this method is executed automatically when you run the application. In this case, the code displays the data the user sees on the console, accepts the data the user enters at the console, and calculates the future value.

The second method is named calculateFutureValue. This method is called from the main method and calculates the future value based on the data the user enters.

The code for the Future Value application

import java.util.Scanner;
import java.text.NumberFormat;
public class FutureValueApp
public static void main(String[] args)
System.out.println("\nWelcome to the Future Value Calculator\n");
Scanner sc = new Scanner(;
String choice = "y";
while (choice.equalsIgnoreCase("y"))
// get the input from the user
System.out.print("Enter monthly investment: ");
double monthlyInvestment = sc.nextDouble();
System.out.print("Enter yearly interest rate: ");
double interestRate = sc.nextDouble();
System.out.print("Enter number of years: ");
int years = sc.nextInt();
// calculate the future value
double monthlyInterestRate = interestRate/12/100;
int months = years * 12;
double futureValue = calculateFutureValue(
monthlyInvestment, monthlyInterestRate, months);
// format and display the result
NumberFormat currency = NumberFormat.getCurrencyInstance();
System.out.println("Future value: " +
currency.format(futureValue) + "\n");
// see if the user wants to continue
System.out.print("Continue? (y/n): ");
choice =;
private static double calculateFutureValue(double monthlyInvestment,
double monthlyInterestRate, int months)
double futureValue = 0;
for (int i = 1; i <= months; i++)
futureValue = (futureValue + monthlyInvestment) *
(1 + monthlyInterestRate);
return futureValue;

Figure 2: The code for the console version of the Future Value application

How Java Compiles and Interprets Code
When you develop a Java application, you create one or more classes. For each class, you write the Java statements that direct the operation of the class. Then, you use a Java tool to translate the Java statements into instructions that can be run by the computer. This process is illustrated in Figure 3.

To start, you enter and edit the Java source code for a class. These are the Java statements like the ones you saw in Figure 2 that tell the application what to do. Then, you use the Java compiler to compile the source code into a format known as Java bytecodes. At this point, the bytecodes can be run on any platform that has a Java interpreter to interpret (or translate) the Java bytecodes into code that can be understood by the underlying operating system.

Since Java interpreters are available for all major operating systems, you can run Java on most platforms. This is what gives Java applications their platform independence. In contrast, C++ requires a specific compiler for each type of platform that its programs are going to run on. When a platform has a Java interpreter installed on it, it can be considered an implementation of a Java virtual machine (JVM).

In addition, most modern web browsers can be Java enabled. This allows applets, which are bytecodes that are downloaded from the Internet or an intranet, to run within a web browser. To make this work, Sun developed (and Oracle now maintains) the Java Plug-in. This piece of software is similar to other browser plug-ins such as Apple QuickTime. It allows the browser to run the current version of the Java interpreter.

Figure 3: How Java compiles and interprets Code Description

  • When you develop a Java application, you develop one or more classes.
  • You can use a Java IDE or any text editor to create, edit, and save the source code for a Java class. Source code files have the java extension.
  • The Java compiler translates Java source code into a platform-independent format known as Java bytecodes. Files that contain Java bytecodes have the class extension.
  • The Java interpreter executes Java bytecodes. Since Java interpreters exist for all major operating systems, Java bytecodes can be run on most platforms. A Java interpreter is an implementation of a Java virtual machine (JVM).
  • Most modern web browsers can be Java enabled. This lets applets run within these browsers. Oracle provides a tool known as the Java Plug-in that allows you to specify the version of the Java interpreter that you want to use.

•   •   •

This excerpt is from the book Murach's Java Programming by Joel Murach:

More Stories By Joel Murach

Joel Murach has been writing and editing books about computer programming for over 10 years. During that time, he has written extensively on a wide range of Java, .NET, web, and database technologies. When he's not programming or writing books about programming, he can be found surfing or writing music.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.

@ThingsExpo Stories
Cloud computing delivers on-demand resources that provide businesses with flexibility and cost-savings. The challenge in moving workloads to the cloud has been the cost and complexity of ensuring the initial and ongoing security and regulatory (PCI, HIPAA, FFIEC) compliance across private and public clouds. Manual security compliance is slow, prone to human error, and represents over 50% of the cost of managing cloud applications. Determining how to automate cloud security compliance is critical to maintaining positive ROI. Raxak Protect is an automated security compliance SaaS platform and ma...
The Internet of Things (IoT) is growing rapidly by extending current technologies, products and networks. By 2020, Cisco estimates there will be 50 billion connected devices. Gartner has forecast revenues of over $300 billion, just to IoT suppliers. Now is the time to figure out how you’ll make money – not just create innovative products. With hundreds of new products and companies jumping into the IoT fray every month, there’s no shortage of innovation. Despite this, McKinsey/VisionMobile data shows "less than 10 percent of IoT developers are making enough to support a reasonably sized team....
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo 2016 in New York and Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th 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 cha...
Just over a week ago I received a long and loud sustained applause for a presentation I delivered at this year’s Cloud Expo in Santa Clara. I was extremely pleased with the turnout and had some very good conversations with many of the attendees. Over the next few days I had many more meaningful conversations and was not only happy with the results but also learned a few new things. Here is everything I learned in those three days distilled into three short points.
DevOps is about increasing efficiency, but nothing is more inefficient than building the same application twice. However, this is a routine occurrence with enterprise applications that need both a rich desktop web interface and strong mobile support. With recent technological advances from Isomorphic Software and others, rich desktop and tuned mobile experiences can now be created with a single codebase – without compromising functionality, performance or usability. In his session at DevOps Summit, Charles Kendrick, CTO and Chief Architect at Isomorphic Software, demonstrated examples of com...
As organizations realize the scope of the Internet of Things, gaining key insights from Big Data, through the use of advanced analytics, becomes crucial. However, IoT also creates the need for petabyte scale storage of data from millions of devices. A new type of Storage is required which seamlessly integrates robust data analytics with massive scale. These storage systems will act as “smart systems” provide in-place analytics that speed discovery and enable businesses to quickly derive meaningful and actionable insights. In his session at @ThingsExpo, Paul Turner, Chief Marketing Officer at...
In his keynote at @ThingsExpo, Chris Matthieu, Director of IoT Engineering at Citrix and co-founder and CTO of Octoblu, focused on building an IoT platform and company. He provided a behind-the-scenes look at Octoblu’s platform, business, and pivots along the way (including the Citrix acquisition of Octoblu).
In his General Session at 17th Cloud Expo, Bruce Swann, Senior Product Marketing Manager for Adobe Campaign, explored the key ingredients of cross-channel marketing in a digital world. Learn how the Adobe Marketing Cloud can help marketers embrace opportunities for personalized, relevant and real-time customer engagement across offline (direct mail, point of sale, call center) and digital (email, website, SMS, mobile apps, social networks, connected objects).
We all know that data growth is exploding and storage budgets are shrinking. Instead of showing you charts on about how much data there is, in his General Session at 17th Cloud Expo, Scott Cleland, Senior Director of Product Marketing at HGST, showed how to capture all of your data in one place. After you have your data under control, you can then analyze it in one place, saving time and resources.
Two weeks ago (November 3-5), I attended the Cloud Expo Silicon Valley as a speaker, where I presented on the security and privacy due diligence requirements for cloud solutions. Cloud security is a topical issue for every CIO, CISO, and technology buyer. Decision-makers are always looking for insights on how to mitigate the security risks of implementing and using cloud solutions. Based on the presentation topics covered at the conference, as well as the general discussions heard between sessions, I wanted to share some of my observations on emerging trends. As cyber security serves as a fou...
The Internet of Everything is re-shaping technology trends–moving away from “request/response” architecture to an “always-on” Streaming Web where data is in constant motion and secure, reliable communication is an absolute necessity. As more and more THINGS go online, the challenges that developers will need to address will only increase exponentially. In his session at @ThingsExpo, Todd Greene, Founder & CEO of PubNub, exploreed the current state of IoT connectivity and review key trends and technology requirements that will drive the Internet of Things from hype to reality.
With all the incredible momentum behind the Internet of Things (IoT) industry, it is easy to forget that not a single CEO wakes up and wonders if “my IoT is broken.” What they wonder is if they are making the right decisions to do all they can to increase revenue, decrease costs, and improve customer experience – effectively the same challenges they have always had in growing their business. The exciting thing about the IoT industry is now these decisions can be better, faster, and smarter. Now all corporate assets – people, objects, and spaces – can share information about themselves and thei...
Continuous processes around the development and deployment of applications are both impacted by -- and a benefit to -- the Internet of Things trend. To help better understand the relationship between DevOps and a plethora of new end-devices and data please welcome Gary Gruver, consultant, author and a former IT executive who has led many large-scale IT transformation projects, and John Jeremiah, Technology Evangelist at Hewlett Packard Enterprise (HPE), on Twitter at @j_jeremiah. The discussion is moderated by me, Dana Gardner, Principal Analyst at Interarbor Solutions.
Too often with compelling new technologies market participants become overly enamored with that attractiveness of the technology and neglect underlying business drivers. This tendency, what some call the “newest shiny object syndrome” is understandable given that virtually all of us are heavily engaged in technology. But it is also mistaken. Without concrete business cases driving its deployment, IoT, like many other technologies before it, will fade into obscurity.
Discussions of cloud computing have evolved in recent years from a focus on specific types of cloud, to a world of hybrid cloud, and to a world dominated by the APIs that make today's multi-cloud environments and hybrid clouds possible. In this Power Panel at 17th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the importance of customers being able to use the specific technologies they need, through environments and ecosystems that expose their APIs to make true change and transformation possible.
The Internet of Things is clearly many things: data collection and analytics, wearables, Smart Grids and Smart Cities, the Industrial Internet, and more. Cool platforms like Arduino, Raspberry Pi, Intel's Galileo and Edison, and a diverse world of sensors are making the IoT a great toy box for developers in all these areas. In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists discussed what things are the most important, which will have the most profound effect on the world, and what should we expect to see over the next couple of years.
Microservices are a very exciting architectural approach that many organizations are looking to as a way to accelerate innovation. Microservices promise to allow teams to move away from monolithic "ball of mud" systems, but the reality is that, in the vast majority of organizations, different projects and technologies will continue to be developed at different speeds. How to handle the dependencies between these disparate systems with different iteration cycles? Consider the "canoncial problem" in this scenario: microservice A (releases daily) depends on a couple of additions to backend B (re...
The cloud. Like a comic book superhero, there seems to be no problem it can’t fix or cost it can’t slash. Yet making the transition is not always easy and production environments are still largely on premise. Taking some practical and sensible steps to reduce risk can also help provide a basis for a successful cloud transition. A plethora of surveys from the likes of IDG and Gartner show that more than 70 percent of enterprises have deployed at least one or more cloud application or workload. Yet a closer inspection at the data reveals less than half of these cloud projects involve production...
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it! In her Day 2 Keynote at 17th Cloud Expo, Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, wil...
PubNub has announced the release of BLOCKS, a set of customizable microservices that give developers a simple way to add code and deploy features for realtime apps.PubNub BLOCKS executes business logic directly on the data streaming through PubNub’s network without splitting it off to an intermediary server controlled by the customer. This revolutionary approach streamlines app development, reduces endpoint-to-endpoint latency, and allows apps to better leverage the enormous scalability of PubNub’s Data Stream Network.