Welcome!

Java IoT Authors: Liz McMillan, Elizabeth White, Pat Romanski, William Schmarzo, Stackify Blog

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
SYS-CON Events announced today that Keisoku Research Consultant Co. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Keisoku Research Consultant, Co. offers research and consulting in a wide range of civil engineering-related fields from information construction to preservation of cultural properties. For more information, vi...
SYS-CON Events announced today that Interface Corporation will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Interface Corporation is a company developing, manufacturing and marketing high quality and wide variety of industrial computers and interface modules such as PCIs and PCI express. For more information, visit http://www.i...
SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
SYS-CON Events announced today that Fusic will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Fusic Co. provides mocks as virtual IoT devices. You can customize mocks, and get any amount of data at any time in your test. For more information, visit https://fusic.co.jp/english/.
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
SYS-CON Events announced today that Taica will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Taica manufacturers Alpha-GEL brand silicone components and materials, which maintain outstanding performance over a wide temperature range -40C to +200C. For more information, visit http://www.taica.co.jp/english/.
Join IBM November 1 at 21st Cloud Expo at the Santa Clara Convention Center in Santa Clara, CA, and learn how IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Cognitive analysis impacts today’s systems with unparalleled ability that were previously available only to manned, back-end operations. Thanks to cloud processing, IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Imagine a robot vacuum that becomes your personal assistant th...
In his session at @ThingsExpo, Greg Gorman is the Director, IoT Developer Ecosystem, Watson IoT, will provide a short tutorial on Node-RED, a Node.js-based programming tool for wiring together hardware devices, APIs and online services in new and interesting ways. It provides a browser-based editor that makes it easy to wire together flows using a wide range of nodes in the palette that can be deployed to its runtime in a single-click. There is a large library of contributed nodes that help so...
SYS-CON Events announced today that Daiya Industry will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Daiya Industry specializes in orthotic support systems and assistive devices with pneumatic artificial muscles in order to contribute to an extended healthy life expectancy. For more information, please visit https://www.daiyak...
What is the best strategy for selecting the right offshore company for your business? In his session at 21st Cloud Expo, Alan Winters, U.S. Head of Business Development at MobiDev, will discuss the things to look for - positive and negative - in evaluating your options. He will also discuss how to maximize productivity with your offshore developers. Before you start your search, clearly understand your business needs and how that impacts software choices.
SYS-CON Events announced today that SIGMA Corporation will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. uLaser flow inspection device from the Japanese top share to Global Standard! Then, make the best use of data to flip to next page. For more information, visit http://www.sigma-k.co.jp/en/.
SYS-CON Events announced today that Yuasa System will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Yuasa System is introducing a multi-purpose endurance testing system for flexible displays, OLED devices, flexible substrates, flat cables, and films in smartphones, wearables, automobiles, and healthcare.
SYS-CON Events announced today that B2Cloud will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. B2Cloud specializes in IoT devices for preventive and predictive maintenance in any kind of equipment retrieving data like Energy consumption, working time, temperature, humidity, pressure, etc.
SYS-CON Events announced today that NetApp has been named “Bronze Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. NetApp is the data authority for hybrid cloud. NetApp provides a full range of hybrid cloud data services that simplify management of applications and data across cloud and on-premises environments to accelerate digital transformation. Together with their partners, NetApp em...
SYS-CON Events announced today that Ryobi Systems will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ryobi Systems Co., Ltd., as an information service company, specialized in business support for local governments and medical industry. We are challenging to achive the precision farming with AI. For more information, visit http:...
SYS-CON Events announced today that mruby Forum will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. mruby is the lightweight implementation of the Ruby language. We introduce mruby and the mruby IoT framework that enhances development productivity. For more information, visit http://forum.mruby.org/.
SYS-CON Events announced today that Mobile Create USA will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Mobile Create USA Inc. is an MVNO-based business model that uses portable communication devices and cellular-based infrastructure in the development, sales, operation and mobile communications systems incorporating GPS capabi...
SYS-CON Events announced today that Enroute Lab will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Enroute Lab is an industrial design, research and development company of unmanned robotic vehicle system. For more information, please visit http://elab.co.jp/.
Real IoT production deployments running at scale are collecting sensor data from hundreds / thousands / millions of devices. The goal is to take business-critical actions on the real-time data and find insights from stored datasets. In his session at @ThingsExpo, John Walicki, Watson IoT Developer Advocate at IBM Cloud, will provide a fast-paced developer journey that follows the IoT sensor data from generation, to edge gateway, to edge analytics, to encryption, to the IBM Bluemix cloud, to Wa...
SYS-CON Events announced today that Nihon Micron will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Nihon Micron Co., Ltd. strives for technological innovation to establish high-density, high-precision processing technology for providing printed circuit board and metal mount RFID tags used for communication devices. For more inf...