TweetFollow Us on Twitter

Java Grids
Volume Number:12
Issue Number:11
Column Tag:Getting Started

Two Java Grid Layouts

By Dave Mark

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

Last month, we introduced the Java Layout Manager and saw the power of layouts combined with panels. This month, we’ll look at two important layout classes, GridLayout and GridBagLayout, and present a series of applets that bring these two classes to life.

There is a newly reformatted set of Java API documentation, collectively known as the 1.0.2 API. If you don’t already have this, go get it now. The URL is:

http://java.sun.com/doc/api_documentation.html

There are two Mac download links on this page. Though it’s bigger, you might try the .hqx file (as opposed to the .bin file). I’m not sure why, but when I downloaded the .bin file and dropped it on StuffIt Expander, the final .sea file was corrupted. On the other hand, by the time you read this, the problem most likely will have been corrected.

GridLayout

As its name implies, the GridLayout lays out its components in a grid. GridLayout has two constructors:

public GridLayout( int  rows, int  cols );

This one creates a grid layout with the specified rows and columns. As you’ll see, GridLayout does the best it can to lay the current set of components out in this configuration. But what if you have too few components? Or too many? This month’s sample applets are ideal for experimenting.

The second constructor adds two new parameters:

public GridLayout( int  rows, int  cols,
                   int  hgap, int  vgap );

This version creates a grid layout with the specified rows and columns, but also lets you specify a minimal horizontal and vertical gap to appear between the components.

GridLayout is pretty straightforward. Here’s a sample applet to take it for a spin.

• Launch the CodeWarrior IDE and create a new “Java Applet” project called GridLayout.µ.

• Create a new source code window, type in the following source code, save as GridLayout.Java, and add to it the project.

import java.awt.*;

public class MyGrid extends java.applet.Applet
{
 public MyGrid()
 {
 setLayout( new GridLayout( 4, 4 ) );
 
 add( new Button( “1” ) );
 add( new Button( “2” ) );
 add( new Button( “3” ) );
 add( new Button( “4” ) );
 add( new Button( “5” ) );
 add( new Button( “6” ) );
 add( new Button( “7” ) );
 add( new Button( “8” ) );
 add( new Button( “9” ) );
 add( new Button( “10” ) );
 add( new Button( “11” ) );
 add( new Button( “12” ) );
 add( new Button( “13” ) );
 add( new Button( “14” ) );
 add( new Button( “15” ) );
 add( new Button( “16” ) );
 }
}

• Create a second source code window, type in the following HTML, save as GridLayout.html, and add it to the project as well.

<title>GridLayout</title>
<hr>
<applet codebase=”GridLayout Files” code=”MyGrid.class” width=200 height=200>
</applet>
<hr>
<a href=”GridLayout.java”>The source.</a>

• Remove the two <replace me> files from the project (Apple-click on the files to select them, then hit option-delete).

• Edit the project prefs, specifically, the Java Project pane. Set the Project Type popup to “Class Folder” and type “GridLayout Files” (without the quotes) as the Folder Name.

It’s important that the Class Folder preference exactly match the “codebase” attribute in your HTML file.

• Once all your source is in place, select Make from the Project menu to generate your class file.

• To run your applet, drop the html file onto your Java Applet runner or Java-capable browser. Figure 1 shows my version running in a Netscape window.

Figure 1. The GridLayout applet, running in Netscape.

The GridLayout Source Code

Here’s how the source code works. First comes the normal opening stuff, the import statement and class definition. The setLayout() statement creates a new GridLayout object with 4 rows and 4 columns, and makes it the current layout.

import java.awt.*;

public class MyGrid extends java.applet.Applet
{
 public MyGrid()
 {
 setLayout( new GridLayout( 4, 4 ) );

Next, we create a series of 16 buttons and add them to the current frame.

 add( new Button( “1” ) );
 add( new Button( “2” ) );
 add( new Button( “3” ) );
 add( new Button( “4” ) );
 add( new Button( “5” ) );
 add( new Button( “6” ) );
 add( new Button( “7” ) );
 add( new Button( “8” ) );
 add( new Button( “9” ) );
 add( new Button( “10” ) );
 add( new Button( “11” ) );
 add( new Button( “12” ) );
 add( new Button( “13” ) );
 add( new Button( “14” ) );
 add( new Button( “15” ) );
 add( new Button( “16” ) );
 }
}

That’s it! When you run the applet, your 16 buttons will appear in a 4 by 4 grid. The width and height of the buttons is determined by the width and height attributes in your HTML’s applet tag. Make the applet frame wider, the buttons will each be made wider. Make the frame taller, the buttons will each be made taller.

You can also affect the results by changing the parameters you pass to the GridLayout constructor. Experiment.

GridLayout, Version 2

Here’s another GridLayout applet. This one uses all four constructor parameters, and includes a nifty little trick you’ll want to remember. First, here’s the code:

import java.awt.*;

public class MyGrid extends java.applet.Applet
{
 int    numButtons;
 String att;
 
 public void init()
 {
 att = getParameter( “NUMBUTTONS” );
 numButtons = Integer.valueOf(att).intValue();
 
 setLayout( new GridLayout( 2, 20, 5, 20 ) );
 
 for ( int i=1; i<=numButtons; i++ )
 add( new Button( “”+i ) );
 }
}

Next, here’s the HTML:

<title>GridLayout</title>
<hr>
<applet codebase=”GridLayout Files” code=”MyGrid.class” width=400 height=200>
<param name=”NUMBUTTONS” value=”16”>
</applet>
<hr>
<a href=”GridLayout.java”>The source.</a>

Figure 2 shows the applet in action, running under Netscape. Let’s take a look at this source.

Figure 2. Another GridLayout applet using all 4 parameters.

GridLayout 2 Source Code

This version of GridLayout.Java starts off in the same way, but does its creating in init() instead of in MyGrid(). This gives us access to the HTML parameters. I’m not sure why getParameter() doesn’t work from within MyGrid(), but I’ll look into it.

import java.awt.*;

public class MyGrid extends java.applet.Applet
{
 int    numButtons;
 String att;

If you look back at the HTML, you’ll see that we stuck in a parameter with the name “NUMBUTTONS” and a value of “16”. We call getParameter() to pick up the parameter and Integer.valueOf(att).intValue() to convert the returned string to a number. Next, we create a new GridLayout using all 4 parameters and make it the current layout. Note that we’ve specified 2 rows and 20 columns, with 5 pixels horizontally and 20 pixels vertically between components. The Layout Manager uses the row value first for GridLayouts, so the fact that you’ve specified 20 columns really has no affect. Try using 0 for a column value.

 public void init()
 {
 att = getParameter( “NUMBUTTONS” );
 numButtons = Integer.valueOf(att).intValue();
 
 setLayout( new GridLayout( 2, 20, 5, 20 ) );

Now for the cool trick. In our earlier example, we explicitly specified the name of each button using Strings like “1”, “2”, etc. In this case, we add the loop counter, i, to the null string to produce a string representation of the loop counter. Basically, we’ve forced Java to do the typecasting from number to String for us, since the + operator is expecting a String on both sides. Pretty cool, eh?

 for ( int i=1; i<=numButtons; i++ )
 add( new Button( “”+i ) );
 }
}

The GridBagLayout

The GridLayout works pretty well if all your components are the same size. But, suppose you are working with all sorts of elements; some tall, some wide, whatever. In this case, the GridLayout won’t work particularly well (it’ll waste a lot of screen real estate). Fortunately, there is a complex, grid-based class designed to handle variable sized components.

GridBagLayout and its sister class, GridBagConstraints, allow you to customize a layout that allows components to span multiple grid cells. The GridBagConstraints class features a number of variables, each designed to constrain any components added to the current GridBagLayout. Take a look at the GridBagConstraints class declaration:

public  class  Java.awt.GridBagConstraints
    extends  Java.lang.Object
    implements Java.lang.Cloneable
{
        // Fields
    public int anchor;
    public int fill;
    public int gridheight;
    public int gridwidth;
    public int gridx;
    public int gridy;
    public Insets insets;
    public int ipadx;
    public int ipady;
    public double weightx;
    public double weighty;

        // the anchor field has one of the following values     
    public final static int CENTER;
    public final static int EAST;
    public final static int NORTH;
    public final static int NORTHEAST;
    public final static int NORTHWEST;
    public final static int SOUTH;
    public final static int SOUTHEAST;
    public final static int SOUTHWEST;
    public final static int WEST;

        // the fill field has one of the following values       
    public final static int BOTH;
    public final static int HORIZONTAL;
    public final static int NONE;
    public final static int VERTICAL;

        // default value for gridheight, gridwidth
    public final static int REMAINDER;

        // default value for gridx, gridy
    public final static int RELATIVE;

        // Constructors
    public GridBagConstraints();

        // Methods
    public Object clone();
}

To use a GridBagLayout, you’ll create a GridBagLayout object along with a corresponding GridBagConstraints object, then make the GridBagLayout the current object. Next, you’ll set your GridBagConstraints fields to the settings you prefer. Now you are ready to start adding components to the current frame. All the added components will be formatted according to the current GridBagConstraints settings. Change the constraints settings and add some more components. The changed constraints only affect future components, not the components that were already added.

anchor determines where, within a cell, the component is placed. fill determines if the component is reissued to fill its cell and, if so, how. gridheight specifies the number of cells in a column. gridwidth specifies the number of cells in a row. REMAINDER is used to mark a component as the last in its row or column. RELATIVE is used to mark a component as next to last.

gridx and gridy allow you to specify where to place the component in the grid. A value of (0,0) will put the next component in the upper left corner. A value of RELATIVE will put the component either at the end of a row (in the case of gridx) or column (in the case of gridy).

insets specifies the number of pixels of padding on any side of a cell. ipadx and ipady allow you to specify the padding in pixels within a cell.

Finally, weightx and weighty allow you to specify how much horizontal and vertical space this component should consume when the available extra display area is divvied up between all the components in a row or column.

A GridBagLayout Example

There is really no way to truly appreciate the GridBagLayout without playing with an example. The following is one of the standard Sun applets, stripped down to make it as small as possible. Take some time to play with this applet. Change the constraints, experiment with all the fields and settings to see what they do.

Here’s the source code:

import java.awt.*;

public class MyGridBag extends java.applet.Applet
{
 public MyGridBag()
 {
 GridBagLayout   gridBag = new GridBagLayout();
 GridBagConstraintsconstraints =
                new GridBagConstraints();
 
 setLayout( gridBag );
 
 constraints.fill  =  constraints.BOTH;
 constraints.weightx  =  1.0;

 ConstrainedButton(“Button1”,  gridBag,  constraints );
 ConstrainedButton(“Button2”,  gridBag,  constraints );
 ConstrainedButton(“Button3”,  gridBag,  constraints );

 constraints.gridwidth  =  constraints.REMAINDER;  

 ConstrainedButton(“Button4”,  gridBag,  constraints );

 constraints.weightx  =  0.0;

 ConstrainedButton(“Button5”,  gridBag,  constraints );
 
 constraints.gridwidth  =  constraints.RELATIVE;
 
 ConstrainedButton(“Button6”,  gridBag,  constraints );
 
 constraints.gridwidth  =  constraints.REMAINDER;
 
 ConstrainedButton(“Button7”,  gridBag,  constraints );
 
 constraints.gridwidth  =  1;
 constraints.gridheight  =  2;
 constraints.weighty  =  1.0;
 
 ConstrainedButton(“Button8”,  gridBag,  constraints );
 
 constraints.weighty  =  0.0;
 constraints.gridwidth  =  constraints.REMAINDER;  
 constraints.gridheight  =  1;
 
 ConstrainedButton(“Button9”,  gridBag,  constraints );
 ConstrainedButton(“Button10”,  gridBag,  constraints );
 }
 
 void ConstrainedButton( String title,
 GridBagLayout layout, GridBagConstraints constraints )
 {
 Button button = new Button( title );
 layout.setConstraints( button, constraints );
 add( button );
 }
}

Here’s the HTML:

<title>GridBagLayout</title>
<hr>
<applet codebase=”GridBagLayout Files” code=”MyGridBag.class” width=400 
height=100>
</applet>
<hr>
<a href=”GridBagLayout.java”>The source.</a>

Figure 3 shows the results of this applet, when run in Netscape.

Figure 3. The classic GridBagLayout applet from Sun.

Till Next Month...

As you go through the GridBagLayout source, pay attention to the use of REMAINDER and RELATIVE. Remember, you are marking a component as 2nd to last and last in its row or column. For example, Button4 should be the last in its row. Button6 should be RELATIVE (2nd to last) while Button7 should be REMAINDER (last). All the buttons should use a gridheight of 1 except for Button8, which will use a gridheight of 2. You get the idea.

Next month, we’ll take a look at double-buffered animation, something that Java makes fairly easy to do. Till then, have a Happy Thanksgiving and save me a wishbone...

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

How to win big in Slots Deluxe
Cheating while gambling is illegal and morally wrong, and in some parts of the world it leads to men with names like Vinnie "Six Knuckles" Manchenzo beating you to a pulp in a dark alley. [Read more] | Read more »
How to take over the world in Dictator 2
Running a country isn't easy - especially when you're a dictator who wants to take over the world and crush everyone in your path while you do it. [Read more] | Read more »
Tips and tricks to get a higher score in...
Tank.iois - you guessed it! - another multiplayer arena battler likeAgar.io and Slither.io. It does differentiate itself by putting you in a tiny tank though, so it's not exactly the same. To help you get that all-important high score, we've got a... | Read more »
How to unlock characters in One Tap Tenn...
As the title suggests, One Tap Tennis requires only a single tap to play its particular brand of tennis, and rewards you with a ton of unlockable characters if you perform well. Fortunately for you, we at 148Apps have got a few tips and tricks to... | Read more »
Grab it now: Game Craft’s Legend of War...
The real time strategy game is now available for you to sink your teeth into, through the App Store and Google Play. Combining elements of skill, strategy and empire building, Legend of War is a real gamers’ game. [Read more] | Read more »
Skateboard Party 3 ft. Greg Lutzka (Gam...
Skateboard Party 3 ft. Greg Lutzka 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Skateboard Party is back! This third edition of the popular sports franchise features professional skater... | Read more »
Cubious (Games)
Cubious 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Cubious – How smart are you? How high is your IQube? Solve the impossible puzzles to find out, and help a lost little cube find his... | Read more »
Goat Simulator Waste of Space (Games)
Goat Simulator Waste of Space 1.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.1 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICESiPhone 4S, iPad 2, iPod Touch 5 or better.** | Read more »
Wildfulness - Unwind in nature and calm...
Wildfulness - Unwind in nature and calm your mind with nature sounds and illustrations 1.0 Device: iOS Universal Category: Healthcare & Fitness Price: $1.99, Version: 1.0 (iTunes) Description: Spending time in nature helps you to... | Read more »
Dr. Panda Racers (Education)
Dr. Panda Racers 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: STEP ON THE GAS, RACE AND WIN!Fasten your seat belts and get ready to race! Speed your way to the finish line while doing... | Read more »

Price Scanner via MacPrices.net

Enterprise Workers Pick Technology Over Perks...
New Adobe study shows surprising attitudes about office jobs and where the future of work is heading. Adobe has released survey findings revealing that a surprising 70 percent of U.S. office workers... Read more
Goal Zero and OtterBox Partner to Expand iPh...
Goal Zero, specialists in portable power, have announced a partnership with OtterBox, brand smartphone case protection, to offer the Slide and Slide Plus Batteries as modules compatible with the new... Read more
15-inch Retina MacBook Pros on sale for up to...
B&H Photo has 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz Retina... Read more
Clearance 2015 13-inch MacBook Airs available...
B&H Photo has clearance 2015 13″ MacBook Airs available for $250 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/4GB/128GB MacBook Air (MJVE2LL/A): $799... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more
21-inch iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ iMacs on sale for up to $120 off MSRP including free shipping plus NY sales tax only: - 21″ 3.1GHz iMac 4K: $1379.99 $120 off MSRP - 21″ 2.8GHz iMac: $1189 $110 off MSRP - 21″ 1... Read more
Kanex Introduces GoPower USB-C Rechargeable B...
Kanex has announced its GoPower USB-C portable battery for the USB-C MacBook, featuring the new industry standard connector and cable used for connectivity and power. Providing users with a new... Read more
Convertible and Detachable Devices Winning Ov...
According to the latest figures published by International Data Corporation (IDC), Western European shipments of ultraslim convertibles and detachables posted positive growth (44.7%) to account for... Read more
New MacBook Pros And Will MacBook Air Be Upgr...
With my mid-2013 13-inch MacBook Air closing on its third anniversary come November, I’m in system upgrade mode. Actually the Haswell CPU equipped Air is still doing a fine job, but my good wife is... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free, and... Read more

Jobs Board

*Apple* Project Engineer - Smart Source Inc...
SmartSource is in need of an Apple Project Engineer for a 12 month contract opportunity in Pittsburg, PA. Role: Apple Project Engineer Location: Pittsburg, PA Read more
Automotive Sales Consultant - Apple Ford Linc...
…you. The best candidates are smart, technologically savvy and are customer focused. Apple Ford Lincoln Apple Valley is different, because: $30,000 annual salary Read more
Service Assistant - *Apple* Chevrolet *App...
Apple Automotive is one of the fastest growing dealer...and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive, we Read more
Editor, *Apple* News - APPLE (United States...
Job Summary The Apple News team is looking for a passionate and knowledgeable editor with experience covering entertainment/pop culture and experience running social Read more
*Apple* Nissan Service Technicians - Apple A...
Apple Automotive is one of the fastest growing dealer...and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive , Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.