Home > Articles > Programming > Java

Creating Window Interfaces Using Swing Objects

Walter Savitch teaches you how to write Java programs that create such modern windowing interfaces for input and output using a special library of classes called Swing.
This sample chapter is excerpted from Java: An Introduction to Computer Science & Programming, by Walter Savitch.
This chapter is from the book

Window Interfaces Using Swing Objects

"What is the use of a book," thought Alice, "without pictures or conversations?"
Lewis Carroll, Alice's Adventures in Wonderland

So far, almost all your programs have used the simplest form of input. The user enters simple text at the keyboard; and simple, unadorned text is sent to the screen as output. We have kept the input and output simple to concentrate on other basic features of programming and the Java language. But, modern programs do not use such simple input and output.

Modern programs use windowing interfaces with such features as menus and buttons that allow the user to make choices with a mouse. In this article, you will learn how to write Java programs that create such modern windowing interfaces for input and output using a special library of classes called Swing. Swing is a standard library that comes with all versions of Java 2 (also known as JDK 1.2 and as SDK 1.2). (Higher-numbered versions should also include the Swing library.) Entire books have been written on Swing, and so we will not have room to give you a complete description of Swing. However, in this article we will teach you enough to allow you to write simple windowing interfaces.

Swing is part of a larger collection of classes known as the Java Foundation Classes, or JFC. For what we are doing here, you do not need to be aware of anything about the JFC other than what we will tell you about Swing. However, if you hear about the JFC, you should be aware that you know something about the JFC, namely whatever you learn about Swing.

There is another, older library of classes for writing windowing interfaces. This older library is known as the Abstract Windows Toolkit, or AWT for short. Swing can be viewed as an improved version of the AWT. However, Swing did not replace the AWT. Swing added to the AWT to produce a richer collection of classes, and the AWT remains as a necessary complement to the Swing library. We will use classes from both Swing and the AWT. However, you will not go too far wrong if you think of them as all part of a single (larger) Swing library.

(If you are already familiar with the AWT, you will find that programming for Swing is very similar to programming with the AWT. In fact, in many situations the only difference is the spelling of some class names. If you are not familiar with the AWT, do not worry. We assume no knowledge of the AWT.)

Background

event n. 1. An occurrence, incident, or experience, especially one of some significance.
The American Heritage Dictionary of the English Language, First Edition

Let's begin with some general background about the elements in any windowing interface, and about a programming technique known as event-driven programming, which is used when writing windowing interfaces.

GUIs: Graphical User Interfaces

Windowing systems that interact with the user are often called GUIs. GUI is pronounced "gooey" and stands for graphical user interface. The words are pretty much self-explanatory. It's called graphical because it uses graphical elements such as windows, buttons, and menus. It's called a user interface because it is the part of a program that interfaces with (that is, interacts with) the user. A GUI obtains information from the user and gives it to the program for processing. When the program is finished processing the information, the GUI gives the results to the user, usually in some sort of window.

Let's just briefly list the terms used for some basic elements that make up a GUI. Although you have undoubtedly used all these elements before, you may not have given them the same names we will use. A window is a portion of the user's screen that serves as a smaller screen within the screen. A window usually has a border defining its outside edges and a title of some sort giving the window a name. Inside a window you may have smaller window-like objects. Some of these smaller window-like objects are menus. A menu is a list of alternatives offered to the user, usually by offering a list of names. The user chooses one of these alternatives, usually by clicking it with a mouse. A button is very similar to an entry in a menu. A button is simply something that looks like a button to be pushed and that typically has a label. To "push" the button, you use your mouse to click on the button. These elements will have more precise definitions within Swing, but these are the basic properties they have within any windowing system.

Event-Driven Programming

Swing programs and most other graphical user interface (GUI) programs use events and event handlers. An event in a graphical user interface is an object that represents some action such as clicking a mouse, dragging the mouse, pressing a key on the keyboard, clicking the close-window button on a window, or any other action that is expected to elicit a response. Actually, events are more general than just the events of a graphical user interface. For example, a message from a printer to the operating system saying that the printer is ready to print another document can be considered an event. However, in this article, the only events that we will be concerned with are those generated within a graphical user interface.

When an object generates an event, it is called firing the event. In Swing, every object that can fire events, such as a button that might be clicked, can have one or more listener objects. You the programmer specify what objects are the listener objects for any given object that might fire an event. For example, if you click a button, that fires an event, and if the button has a listener object associated with it, then the event is automatically sent to this listener object. A listener object has methods that specify what will happen when events of various kinds are sent to the listener. These methods that handle events are called event handlers. You the programmer will define (or redefine) these event-handler methods.

Notice that event-driven programming is very different from the sort of programming we've seen before now. All our previous programs consisted of a list of statements executed in some order. There were some variations on this theme of performing a list of statements: Loops repeat statements, branches choose one of a list of statements to do next, and a method invocation brings in a different list of statements to be executed. However, at some level, all the programs we have seen so far were designed to be performed by one agent (the computer) following a simple set of instructions of the form "first do this, then do that, then do something else, and so forth."

Event-driven programming is a very different game. In event- driven programming, you create objects that can fire events and you create listener objects to react to the events. For the most part, your program does not determine the order in which things happen. The events determine that order. When an event-driven program is running, the next thing that happens depends on the next event.

Listener objects are almost like people sitting around a room waiting for phone calls. Each person has her or his own phone. When the phone rings, the person with that phone answers and does whatever the phone call says to do. Maybe the message says, "Joe this is your mother calling, I want you to close the window in your room." Then, Joe goes home and closes the window in her or his room. In a graphical user interface, the message is something like "close the window" or "The 'A' key has been pressed" or "The mouse was dragged" from someplace to someplace else. When an event is fired, it is automatically sent to the listener object(s) for the particular object that fired the event. The listener object then calls the appropriate event-handling method to handle the event.

If you have never done event-driven programming before, one aspect of event- driven programming may seem strange to you: You will be writing definitions for methods that you will never invoke in any program. This may seem strange, because a method is of no value unless it is invoked. So somebody or something other than you the programmer must be invoking these methods. That is exactly what does happen. The Swing system automatically invokes certain methods when an event signals that the method needs to be called.

The event-driven programming that we will be doing with the Swing library makes extensive use of inheritance. The classes that you define will be derived classes of some basic predefined classes that are in the Swing library. When you define these classes, they will inherit methods from their parent class. Some of these inherited methods will work fine just as they were written for the parent class (base class). However, often it will be necessary to override a method definition to provide a new definition that is appropriate to the derived class.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020