Welcome!

Java IoT Authors: Gerardo A Dada, Liz McMillan, Carmen Gonzalez, JP Morgenthal, Pat Romanski

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 www.murach.com.

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(System.in);
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 = sc.next();
System.out.println();
}
}
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: http://www.murach.com/books/javp/index.htm

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
What happens when the different parts of a vehicle become smarter than the vehicle itself? As we move toward the era of smart everything, hundreds of entities in a vehicle that communicate with each other, the vehicle and external systems create a need for identity orchestration so that all entities work as a conglomerate. Much like an orchestra without a conductor, without the ability to secure, control, and connect the link between a vehicle’s head unit, devices, and systems and to manage the ...
An IoT product’s log files speak volumes about what’s happening with your products in the field, pinpointing current and potential issues, and enabling you to predict failures and save millions of dollars in inventory. But until recently, no one knew how to listen. In his session at @ThingsExpo, Dan Gettens, Chief Research Officer at OnProcess, discussed recent research by Massachusetts Institute of Technology and OnProcess Technology, where MIT created a new, breakthrough analytics model for ...
IoT is rapidly changing the way enterprises are using data to improve business decision-making. In order to derive business value, organizations must unlock insights from the data gathered and then act on these. In their session at @ThingsExpo, Eric Hoffman, Vice President at EastBanc Technologies, and Peter Shashkin, Head of Development Department at EastBanc Technologies, discussed how one organization leveraged IoT, cloud technology and data analysis to improve customer experiences and effici...
Everyone knows that truly innovative companies learn as they go along, pushing boundaries in response to market changes and demands. What's more of a mystery is how to balance innovation on a fresh platform built from scratch with the legacy tech stack, product suite and customers that continue to serve as the business' foundation. In his General Session at 19th Cloud Expo, Michael Chambliss, Head of Engineering at ReadyTalk, discussed why and how ReadyTalk diverted from healthy revenue and mor...
The 20th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held June 6-8, 2017, at the Javits Center in New York City, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Containers, 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 opportunity. Submit your speaking proposal ...
In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lead...
The Internet of Things (IoT) promises to simplify and streamline our lives by automating routine tasks that distract us from our goals. This promise is based on the ubiquitous deployment of smart, connected devices that link everything from industrial control systems to automobiles to refrigerators. Unfortunately, comparatively few of the devices currently deployed have been developed with an eye toward security, and as the DDoS attacks of late October 2016 have demonstrated, this oversight can ...
You have great SaaS business app ideas. You want to turn your idea quickly into a functional and engaging proof of concept. You need to be able to modify it to meet customers' needs, and you need to deliver a complete and secure SaaS application. How could you achieve all the above and yet avoid unforeseen IT requirements that add unnecessary cost and complexity? You also want your app to be responsive in any device at any time. In his session at 19th Cloud Expo, Mark Allen, General Manager of...
Bert Loomis was a visionary. This general session will highlight how Bert Loomis and people like him inspire us to build great things with small inventions. In their general session at 19th Cloud Expo, Harold Hannon, Architect at IBM Bluemix, and Michael O'Neill, Strategic Business Development at Nvidia, discussed the accelerating pace of AI development and how IBM Cloud and NVIDIA are partnering to bring AI capabilities to "every day," on-demand. They also reviewed two "free infrastructure" pr...
As data explodes in quantity, importance and from new sources, the need for managing and protecting data residing across physical, virtual, and cloud environments grow with it. Managing data includes protecting it, indexing and classifying it for true, long-term management, compliance and E-Discovery. Commvault can ensure this with a single pane of glass solution – whether in a private cloud, a Service Provider delivered public cloud or a hybrid cloud environment – across the heterogeneous enter...
"Dice has been around for the last 20 years. We have been helping tech professionals find new jobs and career opportunities," explained Manish Dixit, VP of Product and Engineering at Dice, in this SYS-CON.tv interview at 19th Cloud Expo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
Extracting business value from Internet of Things (IoT) data doesn’t happen overnight. There are several requirements that must be satisfied, including IoT device enablement, data analysis, real-time detection of complex events and automated orchestration of actions. Unfortunately, too many companies fall short in achieving their business goals by implementing incomplete solutions or not focusing on tangible use cases. In his general session at @ThingsExpo, Dave McCarthy, Director of Products...
"ReadyTalk is an audio and web video conferencing provider. We've really come to embrace WebRTC as the platform for our future of technology," explained Dan Cunningham, CTO of ReadyTalk, in this SYS-CON.tv interview at WebRTC Summit at 19th Cloud Expo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
The many IoT deployments around the world are busy integrating smart devices and sensors into their enterprise IT infrastructures. Yet all of this technology – and there are an amazing number of choices – is of no use without the software to gather, communicate, and analyze the new data flows. Without software, there is no IT. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, Dave McCarthy, Director of Products at Bsquare Corporation; Alan Williamson, Principal...
Businesses and business units of all sizes can benefit from cloud computing, but many don't want the cost, performance and security concerns of public cloud nor the complexity of building their own private clouds. Today, some cloud vendors are using artificial intelligence (AI) to simplify cloud deployment and management. In his session at 20th Cloud Expo, Ajay Gulati, Co-founder and CEO of ZeroStack, will discuss how AI can simplify cloud operations. He will cover the following topics: why clou...
Video experiences should be unique and exciting! But that doesn’t mean you need to patch all the pieces yourself. Users demand rich and engaging experiences and new ways to connect with you. But creating robust video applications at scale can be complicated, time-consuming and expensive. In his session at @ThingsExpo, Zohar Babin, Vice President of Platform, Ecosystem and Community at Kaltura, discussed how VPaaS enables you to move fast, creating scalable video experiences that reach your aud...
"At ROHA we develop an app called Catcha. It was developed after we spent a year meeting with, talking to, interacting with senior citizens watching them use their smartphones and talking to them about how they use their smartphones so we could get to know their smartphone behavior," explained Dave Woods, Chief Innovation Officer at ROHA, in this SYS-CON.tv interview at 19th Cloud Expo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
WebRTC is the future of browser-to-browser communications, and continues to make inroads into the traditional, difficult, plug-in web communications world. The 6th WebRTC Summit continues our tradition of delivering the latest and greatest presentations within the world of WebRTC. Topics include voice calling, video chat, P2P file sharing, and use cases that have already leveraged the power and convenience of WebRTC.
20th Cloud Expo, taking place June 6-8, 2017, at the Javits Center in New York City, NY, 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.
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...