Welcome!

Java IoT Authors: Liz McMillan, Pat Romanski, Elizabeth White, Harry Trott, Scott Allen

Related Topics: Java IoT, Industrial IoT, Microservices Expo, IBM Cloud, Weblogic, Linux Containers, Containers Expo Blog, IT SOLUTIONS GUIDE, Eclipse

Java IoT: Article

Java Basics: Lesson 11, Java Packages and Imports (Live Video Education)

Lesson 11 in the Hugely Popular "Java Basics" Series by JDJ Editorial Board Member Yakov Fain

Java comes with thousands of classes that are organized in packages (similar to files and directories on you disk). Some packages include classes responsible for drawing, while other have classes for the Internet access, and so on. For example the class String is located in the package called java.lang, and the fully qualified name of this class is java.lang.String.

The Java compiler only knows where to find classes that are located in the package java.lang, but there are many other packages with useful classes, and it's your responsibility to let the compiler know where the classes that are used in your program live. For example, the package java.io contains classes responsible for input/output operations, while most of the Swing classes live in the following two packages:


javax.swing
javax.swing.event

It would be annoying to write a full class name every time you use it, for example:

javax.swing.JButton myButton = new javax.swing.JButton();
javax.swing.JFrame myFrame = new javax.swing.JFrame();

To avoid this you can use import statements right above the class declaration line, for example:

import javax.swing.JFrame;
import javax.swing.JButton;

class Calculator{
JButton myButton = new JButton();
JFrame myFrame = new JFrame();
}

These import statements allow you to use short class names like JFrame or JButton, and the Java compiler will know where to find them. Please note, that nothing is actually imported into your program: it's just a name resolution mechanism that helps the compiler to find classes and make your program more readable. If your need to use several classes from the same package, you do not have to list each of them in the import statement, just use the wild card. In the following example the asterisk (*) makes all classes from the package javax.swing visible to your program:

import javax.swing.*;

Still, it's better to use separate import statements, so you can see clearly which classes are imported from a particular package.

When programmers work on large projects that have lots of classes, they usually organize them in different packages. For example, one package can have all classes that display graphical windows, while another can contain data access classes.

Let's create a new project called PingPong in the Eclipse IDE. This project will have classes in two packages: screens and engine. Now create a new class PingPongTable and enter the word screens in the field Package:  

Press the button Finish and Eclipse will generate the code that will include the line with the package name.

package screens;

public class PingPongTable {

public static void main(String[] args) {
}
}

By the way, if your class includes the line with the keyword package, you are not allowed to write anything but the program comments above this line.

Since each package is stored in a different folder on a disk, Eclipse creates the folder called screens and puts the file PinPongTable.java there. Check it out - there should be a folder c:\eclipse\workspace\PingPong\screens on your disk with files PingPongTable.java and PingPongTable.class.

Now create another class called PingPongEngine and enter the word engine as the package name. The PingPong project has two packages now:

Since our two classes are located in two different packages (and folders), the class PingPongTable won't see the class PingPongEngine unless you add the appropriate import statement.

package screens;

import engine.PingPongEngine;

public class PingPongTable {

public static void main(String[] args) {
  PingPongEngine gameEngine = new
      PingPongEngine();
}
}

Java packages not only help better organize your classes, but also can be used to hide their classes from the "foreigners" living in other packages. In Java you can use public, private and protected keywords to specify the access level to a particular method or a class. But if you do not use any of these keywords in the method or class declaration, you'll be able to access them only from the classes located in the same package. We've discussed access levels briefly in Lesson 3 of this series.

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

Comments (5) View Comments

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.


Most Recent Comments
Howard N-H 04/13/05 02:53:31 PM EDT

I'm glad you mentioned the use of interfaces as repositories of constants. While it may not be recommended in the strict sense of why interfaces exist, I've used this technique for years on large projects as a good way of organizing and reusing constants.

static imports 04/12/05 06:23:33 AM EDT

So you can use wildcards in the import? Can you use static import for static classes?

Java Basics series 04/12/05 06:12:49 AM EDT

Will the other 10 lessons be on SYS-CON.TV?

Java Live 04/11/05 10:17:40 AM EDT

Is it Yakov Fain who is speaking at the moment? A live Java lesson - cool!

sundeep 04/11/05 06:43:13 AM EDT

I used this lesson in conjunction with the last one, lesson ten on eclipse IDE and it really helped me

@ThingsExpo Stories
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....
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.
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...
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...
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...
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...
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...
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...
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...
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.
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...
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.
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...
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...
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...
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 & ...
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...
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...