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.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Whitethorn Games combines two completely...
If you have ever gone fishing then you know that it is a lesson in patience, sitting around waiting for a bite that may never come. Well, that's because you have been doing it wrong, since as Whitehorn Games now demonstrates in new release Skate... | Read more »
Call of Duty Warzone is a Waiting Simula...
It's always fun when a splashy multiplayer game comes to mobile because they are few and far between, so I was excited to see the notification about Call of Duty: Warzone Mobile (finally) launching last week and wanted to try it out. As someone who... | Read more »
Albion Online introduces some massive ne...
Sandbox Interactive has announced an upcoming update to its flagship MMORPG Albion Online, containing massive updates to its existing guild Vs guild systems. Someone clearly rewatched the Helms Deep battle in Lord of the Rings and spent the next... | Read more »
Chucklefish announces launch date of the...
Chucklefish, the indie London-based team we probably all know from developing Terraria or their stint publishing Stardew Valley, has revealed the mobile release date for roguelike deck-builder Wildfrost. Developed by Gaziter and Deadpan Games, the... | Read more »
Netmarble opens pre-registration for act...
It has been close to three years since Netmarble announced they would be adapting the smash series Solo Leveling into a video game, and at last, they have announced the opening of pre-orders for Solo Leveling: Arise. [Read more] | Read more »
PUBG Mobile celebrates sixth anniversary...
For the past six years, PUBG Mobile has been one of the most popular shooters you can play in the palm of your hand, and Krafton is celebrating this milestone and many years of ups by teaming up with hit music man JVKE to create a special song for... | Read more »
ASTRA: Knights of Veda refuse to pump th...
In perhaps the most recent example of being incredibly eager, ASTRA: Knights of Veda has dropped its second collaboration with South Korean boyband Seventeen, named so as it consists of exactly thirteen members and a video collaboration with Lee... | Read more »
Collect all your cats and caterpillars a...
If you are growing tired of trying to build a town with your phone by using it as a tiny, ineffectual shover then fear no longer, as Independent Arts Software has announced the upcoming release of Construction Simulator 4, from the critically... | Read more »
Backbone complete its lineup of 2nd Gene...
With all the ports of big AAA games that have been coming to mobile, it is becoming more convenient than ever to own a good controller, and to help with this Backbone has announced the completion of their 2nd generation product lineup with their... | Read more »
Zenless Zone Zero opens entries for its...
miHoYo, aka HoYoverse, has become such a big name in mobile gaming that it's hard to believe that arguably their flagship title, Genshin Impact, is only three and a half years old. Now, they continue the road to the next title in their world, with... | Read more »

Price Scanner via MacPrices.net

B&H has Apple’s 13-inch M2 MacBook Airs o...
B&H Photo has 13″ MacBook Airs with M2 CPUs and 256GB of storage in stock and on sale for up to $150 off Apple’s new MSRP, starting at only $849. Free 1-2 day delivery is available to most US... Read more
M2 Mac minis on sale for $100-$200 off MSRP,...
B&H Photo has Apple’s M2-powered Mac minis back in stock and on sale today for $100-$200 off MSRP. Free 1-2 day shipping is available for most US addresses: – Mac mini M2/256GB SSD: $499, save $... Read more
Mac Studios with M2 Max and M2 Ultra CPUs on...
B&H Photo has standard-configuration Mac Studios with Apple’s M2 Max & Ultra CPUs in stock today and on Easter sale for $200 off MSRP. Their prices are the lowest available for these models... Read more
Deal Alert! B&H Photo has Apple’s 14-inch...
B&H Photo has new Gray and Black 14″ M3, M3 Pro, and M3 Max MacBook Pros on sale for $200-$300 off MSRP, starting at only $1399. B&H offers free 1-2 day delivery to most US addresses: – 14″ 8... Read more
Department Of Justice Sets Sights On Apple In...
NEWS – The ball has finally dropped on the big Apple. The ball (metaphorically speaking) — an antitrust lawsuit filed in the U.S. on March 21 by the Department of Justice (DOJ) — came down following... Read more
New 13-inch M3 MacBook Air on sale for $999,...
Amazon has Apple’s new 13″ M3 MacBook Air on sale for $100 off MSRP for the first time, now just $999 shipped. Shipping is free: – 13″ MacBook Air (8GB RAM/256GB SSD/Space Gray): $999 $100 off MSRP... Read more
Amazon has Apple’s 9th-generation WiFi iPads...
Amazon has Apple’s 9th generation 10.2″ WiFi iPads on sale for $80-$100 off MSRP, starting only $249. Their prices are the lowest available for new iPads anywhere: – 10″ 64GB WiFi iPad (Space Gray or... Read more
Discounted 14-inch M3 MacBook Pros with 16GB...
Apple retailer Expercom has 14″ MacBook Pros with M3 CPUs and 16GB of standard memory discounted by up to $120 off Apple’s MSRP: – 14″ M3 MacBook Pro (16GB RAM/256GB SSD): $1691.06 $108 off MSRP – 14... Read more
Clearance 15-inch M2 MacBook Airs on sale for...
B&H Photo has Apple’s 15″ MacBook Airs with M2 CPUs (8GB RAM/256GB SSD) in stock today and on clearance sale for $999 in all four colors. Free 1-2 delivery is available to most US addresses.... Read more
Clearance 13-inch M1 MacBook Airs drop to onl...
B&H has Apple’s base 13″ M1 MacBook Air (Space Gray, Silver, & Gold) in stock and on clearance sale today for $300 off MSRP, only $699. Free 1-2 day shipping is available to most addresses in... Read more

Jobs Board

Medical Assistant - Surgical Oncology- *Apple...
Medical Assistant - Surgical Oncology- Apple Hill Location: WellSpan Medical Group, York, PA Schedule: Full Time Sign-On Bonus Eligible Remote/Hybrid Regular Apply Read more
Omnichannel Associate - *Apple* Blossom Mal...
Omnichannel Associate - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Read more
Cashier - *Apple* Blossom Mall - JCPenney (...
Cashier - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Blossom Mall Read more
Operations Associate - *Apple* Blossom Mall...
Operations Associate - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Read more
Business Analyst | *Apple* Pay - Banco Popu...
Business Analyst | Apple PayApply now " Apply now + Apply Now + Start applying with LinkedIn Start + Please wait Date:Mar 19, 2024 Location: San Juan-Cupey, PR Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.