Compilation using an extended class...
I'm beginning to program in Java after several years away. I cannot for the life of me see why this is not compiling. I'm reading a Wrox book on Java Server Pages and working examples as I go along. This problem should be a snap but not for me.
I have the following class:
package com.wrox.library;
public class Book
private String title;
public String getTitle()
return title;
public void setTitle(String title)
this.title = title;
public Book()
public Book(String title)
this.title = title;
This compiles just fine. Now I have a class that exends Book class, ChildrenBook. So there is this class:
package com.wrox.library;
public class ChildrenBook extends Book
private int minimumAge;
public int getMinimumAge()
return minimumAge;
public void setMinimumAge(int a)
minimumAge = a;
public String getType()
return "CHILDREN";
public ChildrenBook()
super();
public ChildrenBook(String title)
super(title);
Both these classes are in the same directory and are within the Tomcat directory under the calling JSP file. The error I get is "Cannot find symbol...Book". Why is this?
Edited by: platteco on Sep 30, 2007 10:34 PM
platteco wrote:
Thanks for the tip regarding classpath. I used your template to no avail. Here is what it produced:
$ javac -cp WEB-INF\classes\com\wrox\library\ChildrenBook.java
javac: no source files
Usage: javac <options> <source files>
use -help for a list of possible optionsI said
javac -cp WEB-INF/classes com/wrox/library/ChildrenBook.javaNOT
javac -cp WEB-INF/classes/com/wrox/library/ChildrenBook.javaThe former specifies the javac program that it is to look inside the classpath WEB-INF/classes*, and to compile the source file com/wrox/library/ChildrenBook.java*.
What you did was telling the javac program to look inside the classpath
WEB-INF/classes/com.wrox/library/ChildrenBook.java* (which it will assume ChildrenBook.java is either a directory or a zip/jar file that's unfortunately named so) and to compile the source file ... NADA!
The format of the classpath specification is
javac -cp <classpath> <sourcefile>Edited by: Clem1986 on Oct 1, 2007 11:32 AM for stressing
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* FireFX by Grant Skinner. May 30, 2007
* Visit www.gskinner.com/blog for documentation, updates and more free code.
* You may distribute and modify this class freely, provided that you leave this header intact,
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* Please contact [email protected] for more information.
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* Sets the amount of distortion. 0.1 is little, 1 is chaotic.
* @default 0.4
public function set distortion(value:Number):void {
filtersValid &&= (value == _fadeRate);
_distortion = value;
public function get distortion():Number {
return _distortion;
[Inspectable(defaultValue=0.3,name='flameHeight (0-1)')]
* Sets the how high the flame will burn. 0 is zero gravity, 1 is a bonfire.
* @default 0.3
public function set flameHeight(value:Number):void {
perlinValid &&= (value == _flameHeight);
_flameHeight = value;
public function get flameHeight():Number {
return _flameHeight;
[Inspectable(defaultValue=0.3,name='flameSpread (0-1)')]
* Sets the how much the fire will spread out around the target. 0 is no spread, 1 is a lot.
* @default 0.3
public function set flameSpread(value:Number):void {
filtersValid &&= (value == _flameSpread);
_flameSpread = value;
public function get flameSpread():Number {
return _flameSpread;
[Inspectable(defaultValue=false,name='blueFlame')]
* Indicates whether it should use a blue or red flame.
* @default false
public function set blueFlame(value:Boolean):void {
filtersValid &&= (value == _blueFlame);
_blueFlame = value;
public function get blueFlame():Boolean {
return _blueFlame;
[Inspectable(defaultValue=0,name='smoke (0-1)')]
* Sets the amount of smoke. 0 little, 1 lots.
* @default 0
public function set smoke(value:Number):void {
filtersValid &&= (value == _smoke);
_smoke = value;
public function get smoke():Number {
return _smoke;
[Inspectable(defaultValue='',name='target')]
* Sets the amount of smoke. 0 little, 1 lots.
* @default
public function set targetName(value:String):void {
var targ:DisplayObject = parent.getChildByName(value);
if (targ == null) {
try { targ = parent[value] as DisplayObject; }
catch (e:*) {}
target = targ;
* Defines the shape of the fire. The fire will burn upwards, so it should be near the bottom, and centered in the FireFX component.
* @default
public function set target(value:DisplayObject):void {
_target = value;
clear();
public function get target():DisplayObject {
return _target;
* Clears the fire.
public function clear():void {
if (displayBmp) {
displayBmp.fillRect(displayBmp.rect,0);
* Stops the fire effect after letting it burn down over 20 frames.
public function stopFire():void {
// let the fire burn down for 20 frames:
if (endCount == 0) { endCount = 20; }
private function updateBitmaps():void {
if (displayBmp) {
displayBmp.dispose();
displayBmp = null;
scratchBmp.dispose();
scratchBmp = null;
perlinBmp.dispose();
perlinBmp = null;
displayBmp = new BitmapData(width, height, true, 0);
scratchBmp = displayBmp.clone();
perlinBmp = new BitmapData(width*3, height*3, false, 0);
while (numChildren) { removeChildAt(0); }
addChild(new Bitmap(displayBmp));
updatePerlin();
updateFilters();
bmpsValid = true;
private function updatePerlin():void {
perlinBmp.perlinNoise(30*_distortionScale,20*_distortionScale,1,-Math.random()*1000|0,fals e,true,1|2,false);
perlinBmp.colorTransform(perlinBmp.rect,new ColorTransform(1, 1-_flameHeight*0.5 ,1,1,0,0,0,0));
perlinValid = true;
function updateFilters():void {
if (_blueFlame) {
fireCMF = new ColorMatrixFilter([0.8-0.55*_fadeRate,0,0,0,0,
0,0.93-0.48*_fadeRate,0,0,0,
0,0.1,0.96-0.35*_fadeRate,0,0,
0,0.1,0,1,-25+_smoke*24]);
drawColorTransform = new ColorTransform(0,0,0,1,210,240,255,0);
} else {
fireCMF = new ColorMatrixFilter([0.96-0.35*_fadeRate,0.1,0,0,-1,
0,0.9-0.45*_fadeRate,0,0,0,
0,0,0.8-0.55*_fadeRate,0,0,
0,0.1,0,1,-25+_smoke*24]);
drawColorTransform = new ColorTransform(0,0,0,1,255,255,210,0);
dispMapF = new DisplacementMapFilter(perlinBmp,pnt,1,2,14*_distortion,-30,"clamp");
blurF = new BlurFilter(32*_flameSpread,32*_flameSpread,1);
filtersValid = true;
private function startFire():void {
endCount = 0;
addEventListener(Event.ENTER_FRAME,doFire);
private function doFire(evt:Event):void {
if (_target == null) { return; }
if (!bmpsValid) { updateBitmaps(); }
if (!perlinValid) { updatePerlin(); }
if (!filtersValid) { updateFilters(); }
if (endCount == 0) {
var drawMtx:Matrix = _target.transform.matrix;
drawMtx.tx = _target.x-x;
drawMtx.ty = _target.y-y;
scratchBmp.fillRect(scratchBmp.rect,0);
drawColorTransform.alphaOffset = -Math.random()*200|0;
scratchBmp.draw(_target,drawMtx,drawColorTransform,"add");
scratchBmp.applyFilter(scratchBmp,scratchBmp.rect,pnt,blurF);
displayBmp.draw(scratchBmp,mtx,null,"add");
dispMapF.mapPoint = new Point( -Math.random()*(perlinBmp.width-displayBmp.width)|0, -Math.random()*(perlinBmp.height-displayBmp.height)|0 );
displayBmp.applyFilter(displayBmp,displayBmp.rect,pnt,dispMapF);
displayBmp.applyFilter(displayBmp,displayBmp.rect,pnt,fireCMF);
if (endCount != 0 && --endCount == 0) {
removeEventListener(Event.ENTER_FRAME,doFire);
Then, this is the sample application he gave:
import fl.controls.Slider;
import fl.controls.Label;
import fl.events.SliderEvent;
var params:Array = ["distortion","distortionScale","fadeRate","flameHeight","flameSpread","smoke"]
var l:uint = params.length;
for (var i:uint=0; i<l; i++) {
var label:TextField = new TextField();
label.textColor = 0;
label.text = params[i];
label.width = 140;
label.x = 350;
label.y = 55+50*i;
addChild(label);
label = new TextField();
label.textColor = 0x999999;
label.text = "0.35";
label.name = params[i]+"fld";
label.width = 30;
label.x = 490;
label.y = 55+50*i;
addChild(label);
var slider:Slider = new Slider();
slider.name = params[i];
slider.minimum = -2;
slider.maximum = 2;
slider.addEventListener(SliderEvent.THUMB_DRAG,handleSlider);
addChild(slider);
slider.x = 350;
slider.width = 170;
slider.y = 75+50*i;
slider.snapInterval = 0.05;
slider.value = 0.35;
fireFX[params[i]] = 0.35;
function handleSlider(evt:SliderEvent):void {
fireFX[evt.target.name] = evt.target.value;
(getChildByName(evt.target.name+"fld") as TextField).text = String(evt.target.value);
blueFlame.addEventListener(Event.CHANGE,handleCheckBox);
hideText.addEventListener(Event.CHANGE,handleCheckBox);
function handleCheckBox(evt:Event):void {
fireFX.blueFlame = blueFlame.selected;
obj.visible = !hideText.selected;
Thanks again.Looks like he has fireFX instance on the timeline. Most probably this instances symbol base class is com.gskinner.effects.FireFX
You just need to create a directory structure that reflects his package:
com/gskinner/effects/
where you place his FireFX.as
Or, alternatively, you can remove package path from the class header and place FireFx where all you classes (or your application) are:
package com.gskinner.effects {
to
package {
Then you will just need to instantiate the class. -
Than how can i get java class by using it's class file?
Hi
After compilation of a java program, it creates a class file.
After getting class file suppose class file has been deleted.
Than how can i get java class by using it's class file?
Thanks in advance.get a decompiler and run your class file through it--I'll assume you want the source code back and that you are not trying to recover a missing class file by attempting to use the class file that is missing--if it's missing, then I've not a clue on how to get it back by using what is already missing.
BTW: many of your compilers have source control--if it does, just restore your missing file. -
ER unable to compile using javac with java 1.3.1 library (JDEV 10.1.3.0.4)
Hi !
When I try to compile in JDev with javac and the java 1.3.1 library, I get the following error :
Error: javac: invalid flag: -source
The command line generated by JDev looks like :
C:\jdk1.3.1_03\bin\javac.exe -J-mx512m -verbose -deprecation -source 1.3 -target 1.3 -encoding Cp1252 -g -classpath [...] -sourcepath [...] -d [...] @C:\DOCUME~1\user\LOCALS~1\Temp\javac54193.tmp
It seems that -source and -target flags do not exist in this version of javac.
But it does not seem possible to remove these flags generated by JDev, so I'm unable to compile with javac 1.3.1 and JDev.
So i'm looking for :
- A workaround to prevent JDev from adding the -source and -target flags.
- A future release of JDev where you could disable these flags, or, much better, where JDev automatically disables these flags when it detects a 1.3.1 library (there may be other incompatible flags I did not mention).
Thank you for your answers :)Hi,
when you open the project properties and choose the compiler option to tht the compiler to "javac" and then the "source" and "target" to 1.3, wouldn't this compile it for Java 3? I don't think that it is necesary to use JDK 1.3 for compiling the sources
Cross-Compilation Options
By default, classes are compiled against the bootstrap and extension classes of the platform that javac shipped with. But javac also supports cross-compiling, where classes are compiled against a bootstrap and extension classes of a different Java platform implementation. It is important to use -bootclasspath and -extdirs when cross-compiling; see Cross-Compilation Example below.
-target version
Generate class files that will work on VMs with the specified version. The default is to generate class files to be compatible with the 1.2 VM in the Java 2 SDK. The versions supported by javac in the Java 2 SDK are:
1.1
Ensure that generated class files will be compatible with 1.1 and VMs in the Java 2 SDK.
1.2
Generate class files that will run on VMs in the Java 2 SDK, v 1.2 and later, but will not run on 1.1 VMs. This is the default.
1.3
Generate class files that will run on VMs in the Java 2 SDK, v 1.3 and later, but will not run on 1.1 or 1.2 VMs.
1.4
Generate class files that are compatible only with 1.4 VMs.
http://java.sun.com/j2se/1.4.2/docs/tooldocs/windows/javac.html
Frank -
Why class builder allows to develop abstract final class ? What is the use of such class in ABAP?
I am new to ABAP. I tried creating abstract class and found that class builder allows development of abstract final class. What is the use of such class in ABAP?
Hi,
Does not compile:
This one do:
Inheritance:
Regards. -
I am new to Java and for some reason I can't get my head around why to use an abstract class. I understand that an abstract class is something like:
public abstract class Food{ // abstract class
public void eat(){
// stub
public class Apple extends Food{
public void eat(){
// Eat an apple code
}So basically the idea above is that you can eat an "apple" but you can't eat "food" because you can't instantiate an abstract class.
I understand what an abstract class is and how to write one. What I don't understand is why you would use it? It looks to me like I could have just created a normal class called "Food" and just not instantiated it. What are the benefits of using an abstract class?807479 wrote:
I am new to Java and for some reason I can't get my head around why to use an abstract class.One of the first books I ever read about Object-Oriented design contained the following quote from [url http://en.wikipedia.org/wiki/Lucius_Cary,_2nd_Viscount_Falkland]Lord Falkland:
"When it is not necessary to make a decision, it is necessary +not+ to make a decision."
It took me quite a while to understand, but it's all about flexibility: As soon as you cast something in stone, you lose the ability to change it later on if something better/more appropriate comes along. Interfaces and abstract classes are all about delaying that decision.
As jverd said, interfaces allow you to specify what is required without defining the how; and as ErasP said, abstract classes are usually incomplete: ie, they define some of the 'how', but not all of it.
What is most important about abstract classes though is that they cannot exist on their own: They must be extended by a concrete class that completes the 'how' before they can be instantiated and, as such, they declare the intent of the designer.
One of the most important uses of abstract classes is as "skeleton implementations" of interfaces, and there are a lot of examples of these in the Java Collections hierarchy. My favourite is probably AbstractList, which contains a skeleton implementation of a List. Because it exists, I can create a class that wraps an array as a List with very little code, viz:public final class ArrayAsList<T>()
extends AbstractList<T>
private final T[] values;
public ArrayAsList(T... values) {
this.values = values;
@Override
public T get(int index) {
return values[index];
@Override
public T set(int index, T element) {
T value = get(index);
values[index] = element;
return value;
@Override
public int size() {
return values.length;
};and somewhere else, I can use it: List<String> letters =
new ArrayAsList<String>("a", "b", "c");or perhaps, more practically: List<String> words = new ArrayAsList<String>(
bigTextString.split(" +") );Now that may not seem like a big deal to you, but given all that Lists can do, it's actually a very powerful bit of code. The above example is from "Effective Java" (p.95).
HIH
Winston -
Library Projects compiled using Flash Builder and ANT have different outputs
Hi Guys.,
I am really having hard time to get something work right with RSL projects in Flex 3.2 SDK. Here is my weird problem.
I have a library projects which has the following settings in Flash Builder
Link Type : External
airglobal.swc
framework.swc
datavisualization.swc
rpc.swc
utilites.swc
applicationupdater.swc
applicationupdater_ui.swc
Link Type: Merged into code
airframework.swc
servicemonitor.swc
Compiler settings
-directory=true -output=../../lib/core -debug=true -optimize=false -define+=CONFIG::bindingdebug,false -define+=CONFIG::frameworkdebug,false -define+=CONFIG::flexspy,true -define+=CONFIG::debug,true -define+=CONFIG::release,false -define+=CONFIG::logtoconsole,false -allow-source-path-overlap=true -keep-as3-metadata+=Metadata,DefaultProperty,Required,Event,AssignableTo,Inject,InjectCon structor,Publish,Subscribe,PublishSubscribe,Factory,Init,Destroy,Observe,AsyncInit,Managed Events,MessageDispatcher,MessageHandler,MessageBinding,MessageInterceptor,MessageError,Com mand,CommandComplete,CommandResult,CommandError,CommandStatus,ResourceBinding,Selector,Tar get,Autoremove,Internal,ObjectDefinition,DynamicObject
When I compile my library projects I get a MyLibraryproject.swc. The SWC has the following files in it
mx/controls/HTML.png
mx/core/Windows.png
library.swf
Note: airframework.swc and servicemonitor.swc has a many png files and properties files in it. But these properties and png files are not included when compiled in Flash builder.
But when the same project is compiled using ANT compc task, i get all the png and properties files from airframework.swc and servicemonitor.swc files into my library project SWC file.
Here is the ANT version which is used to compile the library project
<compc output="${project.output.dir}/${project.name}.swc"
include-classes="${as} ${mxml}"
use-network="false"
directory="false"
allow-source-path-overlap="true"
incremental="${build.incremental}"
debug="${build.debug}"
locale="${build.locale}"
optimize="false"
>
<define name="CONFIG::bindingdebug" value="${build.bindingdebug}" />
<define name="CONFIG::logtoconsole" value="${build.logtoconsole}" />
<define name="CONFIG::frameworkdebug" value="${build.frameworkdebug}" />
<define name="CONFIG::flexspy" value="${build.flexspy}" />
<define name="CONFIG::debug" value="${build.debug}" />
<define name="CONFIG::release" value="${build.release}" />
<keep-as3-metadata name="Metadata" />
<keep-as3-metadata name="DefaultProperty" />
<keep-as3-metadata name="Required" />
<keep-as3-metadata name="Event" />
<keep-as3-metadata name="AssignableTo" />
<keep-as3-metadata name="Inject" />
<keep-as3-metadata name="InjectConstructor" />
<keep-as3-metadata name="Publish" />
<keep-as3-metadata name="Subscribe" />
<keep-as3-metadata name="PublishSubscribe" />
<keep-as3-metadata name="Factory" />
<keep-as3-metadata name="Init" />
<keep-as3-metadata name="Destroy" />
<keep-as3-metadata name="Observe" />
<keep-as3-metadata name="AsyncInit" />
<keep-as3-metadata name="ManagedEvents" />
<keep-as3-metadata name="MessageDispatcher" />
<keep-as3-metadata name="MessageHandler" />
<keep-as3-metadata name="MessageBinding" />
<keep-as3-metadata name="MessageInterceptor" />
<keep-as3-metadata name="MessageError" />
<keep-as3-metadata name="Command" />
<keep-as3-metadata name="CommandComplete" />
<keep-as3-metadata name="CommandResult" />
<keep-as3-metadata name="CommandError" />
<keep-as3-metadata name="CommandStatus" />
<keep-as3-metadata name="ResourceBinding" />
<keep-as3-metadata name="Selector" />
<keep-as3-metadata name="Target" />
<keep-as3-metadata name="Autoremove" />
<keep-as3-metadata name="Internal" />
<keep-as3-metadata name="ObjectDefinition" />
<keep-as3-metadata name="DynamicObject" />
<load-config filename="${air.config}"/>
<compiler.include-libraries dir="${flex.frameworks.dir}/libs/air" append="true">
<include name="servicemonitor.swc" />
<include name="airframework.swc" />
</compiler.include-libraries>
<external-library-path dir="${build.compc.dir}" append="true">
<include name="TriGeoFlexFramework/TriGeoFlexFramework.swc" />
<include name="TriGeoLibrary/TriGeoLibrary.swc" />
<include name="TriGeoRPCFramework/TriGeoRPCFramework.swc" />
<include name="Degrafa_Beta3.1_Flex3" />
<include name="parsley-flex3-2.4.0.swc" />
<include name="spicelib-flex-2.4.0.swc" />
</external-library-path>
<external-library-path dir="${flex.frameworks.dir}/libs" append="true">
<include name="framework.swc" />
<include name="datavisualization.swc" />
<include name="utilities.swc" />
<include name="rpc.swc" />
<include name="air/airglobal.swc" />
<include name="air/applicationupdater.swc" />
<include name="air/applicationupdater_ui.swc" />
</external-library-path>
<source-path path-element="${basedir}/src" />
</compc>
</target>
</project>
Any insights is greatly appreciated.!#1, If it compiles then you have no issue. There's no reason at this point not to use 4.6. You should bundle a captive runtime to assure the users computer won't need to have AIR installed at all.
#2, Papervision is old. Use the Stage3D and/or a wrapper framework. As far as the generic "If I download lots of data will it take the user more time to load it", well, of course. Just don't make the loading experience painful. Entertain them while they way or find ways of displaying data sooner than later. If it's desirable on the web has more to do with the context of the app and the device displaying it. In other words, a phone user would find it easy but obviously not a desktop user.
#3, Definitely referring you to Google on that one.
#4, Size always matters, it's common sense. The more you process the harder it is. While I haven't done AR I've used the Microsoft Kinect SDK and ANE and tracking was extremely fast but limited. From what I've seen and your basic built in location and direction hardware on any mobile device you shouldn't have much trouble. Depends on what you're doing.
#5, This discussion would be way too large for a forum. You'd need to consult a firm experienced in AR development.
#6, "Applications using the commercial license do not have to provide source code, but must pay a licensing fee. Contact ARToolworks at [email protected] for more information." They will base your price on your product, there is no single price.
#7, The models could be huge and elaborate or tiny and simple which changes the answer. Consult the answer in #4. Ultimately most people are getting on fast networks with mobile and excessively fast on desktop/wifi. Size matters a lot less than 3 years ago.
#8, Depends on what you're doing. You have to explain it.
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