TweetFollow Us on Twitter

Java Layouts
Volume Number:12
Issue Number:10
Column Tag:Getting Started

Java Layouts and Panels

By Dave Mark

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Last month, we explored Peter Lewis’ CWBlink rewrite, which introduced a host of new Java concepts. This month, we’ll start exploring those concepts, starting off with Java Layouts and Panels.

Layouts

In our first few applets, when we wanted to add elements to our main applet frame, we simply added each element directly to the frame, trusting the default applet setup to place things in the applet window in a way that makes sense. This is fine if all you want to do is slap together an interface and you don’t particularly care how it looks.

Being Mac programmers, though, we are all used to a certain way of laying out an interface. You use ResEdit, or Resorcerer, or even a direct toolbox call, and specify the exact pixel location for each interface element. Unfortunately, the Windows and Unix worlds look very different from the Mac world. While all Macs feature square pixels, and a window looks the same no matter what Mac it’s displayed on, Windows and Unix boxes don’t share this consistency.

Since Java is a cross-platform language, Sun needed to come up with a way to represent the interface elements so they would look decent, no matter what machine they appeared on. The solution was a series of layout classes. You use the setLayout() call to attach a layout to a container. The elements in the container are added to the layout depending on the nature of each layout class. This series of example applets should make the value of layouts clear.

Example One: NoLayout.µ

Create a new Java applet project called noLayout.µ. Create a new source file named noLayout.java and add it to the project:

import java.awt.*;

public class noLayout extends java.applet.Applet
{
 public noLayout()
 {
 add( new Label( “Enter your name:” ) );
 add( new TextField( “<Your name here>”, 30 ) );
 add( new Button( “Eeny” ) );
 add( new Button( “Meeny” ) );
 add( new Button( “Miney-Moe” ) );
 }
}

Next, create a second source file called noLayout.html and add it to the project:

<title>No Layout</title>
<hr>
<applet 
 codebase=”noLayout ƒ” 
 code=”noLayout.class” 
 width=530 height=100>
</applet>
<hr>
<a href=”noLayout.java”>The source.</a>

Make the project; then drag the .html file onto the Applet runner (if you are using CodeWarrior, the applet runner is called Metrowerks Java). Figure 1 shows the noLayout applet as it first appears. Notice that all the elements appear in a single row, in the order in which they were added to the default container.

Figure 1. The noLayout applet before resizing

Figure 2 shows what happens when we shrink the window slightly. Notice that the interface elements have “wrapped” to fit comfortably in the new, resized window. Though it is not at all obvious, you are seeing the default layout at work. This default layout is called FlowLayout (see java.awt.FlowLayout.html). You don’t need to create a FlowLayout object for your containing frame. One is created for you. When you call add(), you are adding to a FlowLayout.

Figure 2. The noLayout applet after resizing

FlowLayout treats your elements like words in a word processor. FlowLayout features three constructors. FlowLayout() with no parameters centers all its elements. FlowLayout( int ) takes a single parameter, one of CENTER, LEFT, or RIGHT, which specifies how this FlowLayout should align its elements. Finally, FlowLayout( int align, int hgap, int vgap ) takes three parameters. The first is either CENTER, LEFT, or RIGHT, the second specifies the horizontal minimum gap between elements, and the third specifies the vertical minimum gap between elements.

For the moment, just remember that FlowLayout is the default layout.

Example Two: LayoutNoPanel.µ

Our second example creates a simple, though not particularly useful, layout. Create a new Java applet project called layoutNoPanel.µ. Create a new source file named layoutNoPanel.java and add it to the project:

import java.awt.*;

public class layoutNoPanel extends java.applet.Applet
{
 public layoutNoPanel()
 {
 setLayout( new BorderLayout() );
 
 add( “North”, new Label( “Enter your name:” ) );
 add( “Center”, 
 new TextField(“<Your name here>”, 30) );
 add( “South”, new Button( “Eeny” ) );
 add( “East”, new Button( “Meeny” ) );
 add( “West”, new Button( “Miney-Moe” ) );
 }
}

Next, create a second source file called layoutNoPanel.html and add it to the project:

<title>Layout, No Panel</title>
<hr>
<applet 
 codebase=”layoutNoPanel ƒ” 
 code=”layoutNoPanel.class” 
 width=530 height=100>
</applet>
<hr>
<a href=”layoutNoPanel.java”>The source.</a>

Make the project, then drag the .html file onto the Applet runner. Figure 3 shows the layoutNoPanel applet as it first appears. If you take a look at the source code, you’ll see that a new BorderLayout object is created and made the current layout using setLayout(). The BorderLayout lets you assign items to the top, bottom, left, right, and center using the add() parameters “North”, “South”, “West”, “East”, and “Center”. To learn more about the BorderLayout class and the various constructors you can use to build one, check out java.awt.BorderLayout.html.

Figure 3. The layoutNoPanel applet before resizing

Figure 4 shows what happens when we shrink the window slightly. Notice that the interface elements have all shrunk accordingly. As I said, this wasn’t particularly useful, but it shows an important concept - how to use a layout in your applet code.

Figure 4. The layoutNoPanel applet after resizing

Before proceeding to the last example, see if you can figure out a way to use the FlowLayout and BorderLayout to organize these components into a more useful form Here’s a hint. You’ll want to take advantage of Panels.

Example Three: LayoutWithPanel.µ

Our third example introduces the concept of Panels. Before you examine the code, take a look at java.awt.Panel.html. Think of a Panel as a visual grouping mechanism. The default layout for a Panel is the FlowLayout. We’re going to create a pair of Panels, one to hold the Label and TextField, and the other to hold the three buttons.

Create a new Java applet project called layoutWithPanel.µ. Create a new source file named layoutWithPanel.java and add it to the project:

import java.awt.*;

public class layoutWithPanel 
 extends java.applet.Applet
{
 public layoutWithPanel()
 {
 setLayout( new BorderLayout() );
 
 Panel  top = new Panel();
 Panel  bottom = new Panel();
 
 top.setLayout( new FlowLayout() );
 
 top.add( new Label( “Enter your name:” ) );
 top.add( new TextField( “<Your name here>”, 30 ) );
 
 bottom.setLayout( new FlowLayout() );
 
 bottom.add( new Button( “Eeny” ) );
 bottom.add( new Button( “Meeny” ) );
 bottom.add( new Button( “Miney-Moe” ) );
 
 add( “Center”, top );
 add( “South”, bottom );  
 }
}

Next, create a second source file called layoutWithPanel.html and add it to the project:

<title>Layout, No Panel</title>
<hr>
<applet 
 codebase=”layoutWithPanel ƒ” 
 code=”layoutWithPanel.class” 
 width=530 height=100>
</applet>
<hr>
<a href=”layoutWithPanel.java”>The source.</a>

Make the project, then drag the .html file onto the Applet runner. Figure 5 shows the layoutWithPanel applet as it first appears. Notice that the Label and TextField stick together, and the three buttons stick together.

The source code starts off by creating a BorderLayout. We then create two Panels and add one to the layout as “Center” (the Label and TextField) and one to the layout as “South” (the three buttons).

Figure 5. The layoutWithPanel applet before resizing

Figure 6 shows what happens when we shrink the window slightly. Notice that the TextField wraps to the next line without affecting the three buttons. This is the value of combining Panels with Layouts.

Figure 6. The layoutWithPanel applet after resizing

Till Next Month...

So far, you’ve seen two Layouts - the FlowLayout and the BorderLayout. In next month’s column, we’ll take a look at the remaining Layout classes: GridLayout, GridBagLayout, and CardLayout.

Before we go, I’d like to address a question I get asked all the time: What is the best Java book to buy? Tough question. There’s no simple answer, but I’ll take a shot at it.

I’ve read most of the major Java books. In general, there’s something to like and dislike about every one. Some books offer a really nice writing style, but suffer from buggy or inaccurate code. A good solution is to buy at least two Java books, so you can do a reality check when one book skimps on a topic or contains a bug that perhaps is properly presented in the other.

Though I usually avoid pushing my own books, I would be doing Barry Boone a disservice if I didn’t mention Learn Java on the Macintosh. Though my name tags along on the cover of the book, this is definitely Barry’s baby, and a good introduction to Java. It is also the only Java book that comes with CodeWarrior Lite for Java. I also like Teach Yourself Java In 21 Days by Lemay and Perkins, Java in a Nutshell by Flanagan, and Java Programming Language Handbook by Friedel and Potts.

You could probably get good results with any of these books. Once you get your brain around Java, you should check out The Java Series from Addison-Wesley and Sun. The Java Programming Language is from Ken Arnold and James Gosling. Ken Arnold is a well known C author and, of course, James Gosling created Java. To me, this is sort of like having Kernighan and Ritchie (or, to be more up-to-date, Harbison and Steele) on your C bookshelf.

That being said, there are so many Java books coming out all the time that you should really go down to the bookstore and flip through some of the newer titles and see if any of them strike your fancy. In the meantime, be sure to check out the various Java tutorials on the Web.

 
AAPL
$101.32
Apple Inc.
+0.74
MSFT
$45.15
Microsoft Corpora
-0.07
GOOG
$582.56
Google Inc.
-0.81

MacTech Search:
Community Search:

Software Updates via MacUpdate

Garmin Express 3.2.17.0 - Manage your Ga...
Garmin Express is your essential tool for managing your Garmin devices. Update maps, golf courses and device software. You can even register your device. Update maps Update software Register your... Read more
Audio Hijack Pro 2.11.1 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more
calibre 2.0.0 - Complete e-library manag...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital... Read more
Apple iMovie 10.0.5 - Edit personal vide...
With an all-new design, Apple iMovie lets you enjoy your videos like never before. Browse your clips more easily, instantly share your favorite moments, and create beautiful HD movies and Hollywood-... Read more
Apple Keynote 6.2.2 - Apple's prese...
Apple Keynote makes it simple to create and deliver beautiful presentations. Powerful tools and dazzling effects bring your ideas to life. You can work seamlessly between Mac and iOS devices. And... Read more
Apple Numbers 3.2.2 - Apple's sprea...
With Apple Numbers, sophisticated spreadsheets are just the start. The whole sheet is your canvas. Just add dramatic interactive charts, tables, and images that paint a revealing picture of your data... Read more
OpenOffice 4.1.1 - Free and open-source...
OpenOffice.org is both an Open Source product and a project. The product is a multi-platform office productivity suite. It includes the key desktop applications, such as a word processor,... Read more
Pages 5.2.2 - Apple's word processo...
Apple Pages is a powerful word processor that gives you everything you need to create documents that look beautiful. And read beautifully. It lets you work seamlessly between Mac and iOS devices. And... Read more
Quicken 2015 2.0.1 - Complete personal f...
The new Quicken 2015 helps you manage all your personal finances in one place, so you can see where you're spending and where you can save. Quicken automatically categorizes your financial... Read more
CleanMyMac 2.2.7 - Delete files that was...
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac 2 lets you safely and intelligently scan and clean your entire system, delete large, unused... Read more

Latest Forum Discussions

See All

Trolls vs Vikings Update Adds Over One H...
Trolls vs Vikings Update Adds Over One Hundred Levels, Reduces Item Cost, and More Posted by Ellis Spice on August 22nd, 2014 [ permalink ] | Read more »
SNK Celebrates the 20th Anniversary of T...
SNK Celebrates the 20th Anniversary of The King of Fighters With a Big Sale Posted by Ellis Spice on August 22nd, 2014 [ permalink ] | Read more »
It Came From Canada: Star Wars: Commande...
With a brand new Star Wars trilogy on the horizon, prepare yourselves for Disney and George Lucas’s space fantasy throwback to be more omnipresent than ever before. So it should come as no surprise that new adventures in that galaxy far, far away... | Read more »
Swing Copters Review
Swing Copters Review By Jordan Minor on August 22nd, 2014 Our Rating: :: DIE TRYINGUniversal App - Designed for iPhone and iPad The creator of Flappy Bird is back with a vengeance.   | Read more »
Beam Me an Update Scotty – Star Trek Tre...
Beam Me an Update Scotty – Star Trek Trexels Receives its Biggest Update Yet Posted by Jessica Fisher on August 22nd, 2014 [ permalink ] | Read more »
The Outcast Review
The Outcast Review By Nadia Oxford on August 22nd, 2014 Our Rating: :: HANDS OFF. WAY OFF.Universal App - Designed for iPhone and iPad It’s easy to see what The Outcast is trying for, but its execution needs a lot of work.   | Read more »
HeroCraft Unveils New iOS Game, Marble D...
HeroCraft Unveils New iOS Game, Marble Duel Posted by Jessica Fisher on August 22nd, 2014 [ permalink ] HeroCraft is developing a new chain popper game called Marble Duel, wh | Read more »
Brain+ Review
Brain+ Review By Nadia Oxford on August 22nd, 2014 Our Rating: :: DIM BULBUniversal App - Designed for iPhone and iPad Brain+ is just another entry in an over-saturated brain-training marketplace – and not a particularly fun entry... | Read more »
The Witcher Battle Arena – New Gameplay...
The Witcher Battle Arena – New Gameplay Trailer Revealed Posted by Jessica Fisher on August 22nd, 2014 [ permalink ] Based in the Witcher universe, | Read more »
Max Gentlemen Review
Max Gentlemen Review By Jennifer Allen on August 22nd, 2014 Our Rating: :: OUTSTAYING ITS WELCOMEiPhone App - Designed for the iPhone, compatible with the iPad Max Gentlemen seems pretty quirky initially but that appeal wears thin... | Read more »

Price Scanner via MacPrices.net

Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
Leftover 15-inch 2.0GHz Retina MacBook Pros a...
B&H Photo has leftover previous-generation 15″ 2.0GHz Retina MacBook Pros now available for $1599 including free shipping plus NY sales tax only. Their price is $400 off original MSRP. B&H... Read more
Pro.Calendar – New Productivity App for iPad...
Austin, Texas based mobile business and productivity app developer LightArrow, Inc. has announced Pro.Calendar, a powerful and intuitive calendar app with eight versatile calendar options including... Read more
SanDisk Ultra II SSD — Supercharge Your Syste...
SanDisk Corporation has announced the new SanDisk Ultra II SSD with enhanced SSD Dashboard. The new drive is designed to deliver a cost-effective and easy upgrade solution for PC owners looking to... Read more
Samsung and Barnes & Noble Introduce New...
Samsung Electronics America and NOOK Media, a subsidiary of Barnes & Noble, Inc. have announced the introduction of the new Samsung Galaxy Tab 4 NOOK, a 7-inch tablet combining Samsung’s leading... Read more
21-inch iMacs on sale for up to $150 off MSRP
B&H Photo has 21″ iMacs on sale for up to $150 off MSRP including free shipping plus NY sales tax only. B&H will also include a free copy of Parallels Desktop software: - 21″ 2.7GHz iMac: $... Read more
27-inch 3.2GHz iMac on sale for $1698, save $...
Abt has the 27″ 3.2GHz iMac on sale for $1698 including free shipping. Their price is $101 off MSRP. Read more
Mac Backup Guru 2.0 Drive Backup/Cloneing Uti...
Mac Backup Guru developer MacDaddy has released Mac Backup Guru 2.0, offering new and enhanced advanced features, such as bootable backups, synchronised volumes and folders, and a Snapshot mode that... Read more
Operate GE’s New Free-Standing KItchen Range...
Think you accidentally left the oven on? Switch it off while on the go. The new free-standing Profile™ Series gas and electric ranges are GE’s second cooking appliances, following their wall oven, to... Read more
Parallels Announces Parallels Desktop 10 for...
The no. 1-selling software for running Windows applications on a Mac becomes an even easier choice for millions of consumers and IT professionals worldwide with the launch of the most powerful... Read more

Jobs Board

Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** As businesses discover the power of Apple computers and mobile devices, it's your job - as a Solutions Engineer - to show them how to introduce these Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** At the Apple Store, you connect business professionals and entrepreneurs with the tools they need in order to put Apple solutions to work in their Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.