New to Inner classes
I was wondering the use of Inner classes in real world example with some good example.
Thanks in Advance.
I use Inner Classes to keep the API for my packages
less cluttered, and when there's no current
expectation that the class should ever be instantiated
outside the outter class. Imagine creating JavaDocs
to present to management, and them asking about each
class wondering what it does, and you have to reply to
each one, well that's a helper class that developers
don't need to worry about. Instead, put the classes
where they belong.
Now, like another poster said, if the class has a
chance to be re-used, there isn't really that much
harm in making it outter.Every corpreate class I've taken, or heard of has said exactly what I posted. The easier it is to read the better. Now, using them for arbitrary tasks is one thing, but there is usually a way to get around it. I seen no problem in using that window closing abstract inner class, or abstract inner classes to handle buttons being pressed, but a lot of times there is an easier way to do things to make them more readable. From my experience management likes readability so they can have anyone look at the code to edit if they need to.
Similar Messages
-
Can it be done?
I get:
MyClass.java:21: Type expected.
static class InnerClass extends Panel
For the code
import java.awt.*;
import java.applet.*;
public class MyClass extends Applet {
public MyClass() {
setLayout(new GridLayout(1,2,0,0));
add(new Label("Outer Class"));
InnerClass ic = new InnerClass();
add(ic);
public void init() {
MyClass mc = new MyClass();
static class InnerClass extends Panel {
public InnerClass() {
add(new Label("Inner Class", Label.CENTER));
}1.0?
I know inner classes were added in JDK1.1, I can't remember whether that included static inner classes or whether they were added in 1.2.
Col -
Problem with Outer and Inner Classes....or better way?
Right now I'm trying to create an Inner class.
My .java file compiles ok, and I create my jar file too.
But when I try to instantiate the Inner class, it fails:
java.lang.NoClassDefFoundError: com/myco/vlXML/vlXML$vlDocument.
Here's the class code:
public class vlXML{
private ArrayList myDocList=new ArrayList(); //holds documents
public vlXML(){
private class vlDocument{
public vlDocument(){
//stuff goes here
public vlDocument vlDOC(){
return new vlDocument();
public void addDocument(){
vlXML xxx=new vlXML();
vlDocument myDoc=xxx.vlDOC();
myDocList.add(myDoc);
public int getNumDocs(){
return myDocList.size();
}Then, from a jsp page, I call:
vlXML junk1=new vlXML();
junk1.addDocument();...and get the error...
Can someone help me figure out why it's failing?
Thanks....You nailed it - thanks....(duh!)
While I have your attention, if you don't mind, I have another question.
I'm creating a Class (outer) that allows my users to write a specific XML file (according to my own schema).
Within the XML file, they can have multiple instances of certain tags, like "Document". "Document"s can have multiple fields.
Since I don't know how many "Documents" they may want, I was planning on using an Inner Class of "Document", and then simply letting them "add" as many as necessary (thus the original code posted here).
Does that seem like an efficient (logical/reasonable) methodology,
or is there there something better?
Thanks Again... -
Problem with final variables and inner classes (JDK1.1.8)
When using JDK1.1.8, I came up with following:
public class Outer
protected final int i;
protected Inner inner = null;
public Outer(int value)
i = value;
inner = new Inner();
inner.foo();
protected class Inner
public void foo()
System.out.println(i);
}causing this:
Outer.java:6: Blank final variable 'i' may not have been initialized. It must be assigned a value in an initializer, or in every constructor.
public Outer(int value)
^
1 error
With JDK 1.3 this works just fine, as it does with 1.1.8 if
1) I don't use inner class, or
2) I assign the value in initializer, or
3) I leave the keyword final away.
and none of these is actually an option for me, neither using a newer JDK, if only there is another way to solve this.
Reasons why I am trying to do this:
1) I can't use a newer JDK
2) I want to be able to assign the variables value in constructor
3) I want to prevent anyone (including myself ;)) from changing the value in other parts of the class (yes, the code above is just to give you the idea, not the whole code)
4) I must be able to use inner classes
So, does anyone have a suggestion how to solve this problem of mine? Or can someone say that this is a JDK 1.1.8 feature, and that I just have to live with it? In that case, sticking to solution 3 is probably the best alternative here, at least for me (and hope that no-one will change the variables value). Or is it crappy planning..?You cannot use a final field if you do not
initialize it at the time of declaration. So yes,
your design is invalid.Sorry if I am being a bit too stubborn or something. :) I am just honestly a bit puzzled, since... If I cannot use a final field in an aforementioned situation, why does following work? (JDK 1.3.1 on Linux)
public class Outer {
protected final String str;
public Outer(String paramStr) {
str = paramStr;
Inner in = new Inner();
in.foo();
public void foo() {
System.out.println("Outer.foo(): " + str);
public static void main( String args[] ) {
String param = new String("This is test.");
Outer outer = new Outer(param);
outer.foo();
protected class Inner {
public void foo() {
System.out.println("Inner.foo(): " + str);
} producing the following:
[1:39] % javac Outer.java
[1:39] % java Outer
Inner.foo(): This is test.
Outer.foo(): This is test.
Is this then an "undocumented feature", working even though it shouldn't work?
However, I assume you could
get by with eliminating the final field and simply
passing the value directly to the Inner class's
constructor. if not, you'll have to rethink larger
aspects of your design.I guess this is the way it must be done.
Jussi -
Problem with constructor of inner class.
Hi everybody!
I have an applet which loads images from a database.
i want to draw the images in a textarea, so i wrote an inner class, which extends textarea and overrides the paint method.
but everytime i try to disply the applet in the browser this happens:
java.lang.NoClassDefFoundError: WohnungSuchenApplet$Malfl�che
at java.lang.Class.getDeclaredConstructors0(Native Method)
at java.lang.Class.privateGetDeclaredConstructors(Class.java:1590)
at java.lang.Class.getConstructor0(Class.java:1762)
at java.lang.Class.newInstance0(Class.java:276)
at java.lang.Class.newInstance(Class.java:259)
at sun.applet.AppletPanel.createApplet(AppletPanel.java:567)
at sun.plugin.AppletViewer.createApplet(AppletViewer.java:1778)
at sun.applet.AppletPanel.runLoader(AppletPanel.java:496)
at sun.applet.AppletPanel.run(AppletPanel.java:293)
at java.lang.Thread.run(Thread.java:536)
so my class has no own constructor, it just has the paint method overwritten.
my class looks like this:
public class Malfl�che extends javax.swing.JTextArea{
public void paint(Graphics g){
Color grey=new Color(220,220,220);
g.drawImage(img,10,10,null);
how should a constructor for this class look like?
sorry i am quite new to this, so i really dont have a clue!
my class does not have any attributes or requires any so it doesnt need a constructor, doesnt it?
thanks a lot
timFirst off, unlike regular classes, inner classes can be declared public, private, protected, and default.
Secondly, why are you using the JTextArea to display an image, why not use a JLabel, which takes an Image object as its constructor.
Thirdly, when you drew your image you did not give it a width and height
g.drawImage(img, 0,0, img.getWidth(null), img.getHeight(null), null);
otherwise it will make your image 1 X 1 pixels. not big enough to see. -
Help: Factory Class using Inner Class and Private Constructor?
The situation is as follows:
I want a GamesCollection class that instantiates Game objects by looking up the information needed from a database. I would like to use Game outside of GamesCollection, but only have it instantiated by GamesCollection to ensure the game actually exist. Each Game object is linked to a database record. If a Game object exist, it must also exist in the database. Game objects can never be removed from the database.
I thought about making the Game object an inner class of GamesCollection, but this means that Game class constructor is still visible outside. So what if I made Game constructor private? Well, now I can't create Game objects without a static method inside Game class (static Object factory).
Basically what I need is a constructor for the inner Game class accessible to GamesCollection, but not to the rest of the world (including packages). Is there a way to do this?leesiulung wrote:
As a second look, I was initially confused about your first implementation, but it now makes more sense.
Let me make sure I understand this:
- the interface is needed to make the class accessible outside the outer classBetter: it is necessary to have a type that is accessible outside of GameCollection -- what else could be the return type of instance?
- the instance() method is the object factory
- the private modifier for the inner class is to prevent outside classes to instantiate this objectRight.
However, is a private inner class accessible in the outer class? Try it and see.
How does this affect private/public modifiers on inner classes?Take about five minutes and write a few tests. That should answer any questions you may have.
How do instantiate a GameImpl object? This basically goes back to the first question.Filling out the initial solution:
public interface Game {
String method();
public class GameCollection {
private static class GameImpl implements Game {
public String method() {
return "GameImpl";
public Game instance() {
return new GameImpl();
public static void main(String[] args) {
GameCollection app = new GameCollection();
Game game = app.instance();
System.out.println(game.method());
}Even if you were not interested in controlling game creation, defining interfaces for key concepts like Game is always going to be a good idea. Consider how you will write testing code, for example. How will you mock Game? -
Threaded inner classes & heap memory exhaustion
(_) how can i maximize my threading without running out of
heap memory?
push it to the limit, but throttle back before an
java.lang.OutOfMemoryError.
(_) within 1 threaded class ThreadClass, i have two threaded inner classes. for each instance of ThreadClass i only
start one instance of each inner class.
and, i start hundreds of ThreadClass, but not until the previously running ThreadClass object exits, so only one should be running at any given time.
so, what about threaded inner classes?
are they good? bad? cause "OutOfMemoryErrors"?
are those inner threads not dying?
what are common causes of:
java.lang.OutOfMemoryError: java heap space?
my program runs for about 5-minutes, then
bails with the memory error.
how can i drill down and see what
is eating-up all my memory?
thanks.A Thread class is not the same as a thread of
execution. Those inner class based threads of
execution are not dying.maybe. but this is the way i test a thread's life:
public void run() {
System.out.println("thread start");
System.out.println("thread dies and release memory");
}for each inner thread, and the outer thread, this approach for
testing thread life reveals that they die.
Why don't you use a thread pool?ok. i will think about how to do this.
>
If not, you need to ensure those inner threads have
exited and completed.what is a 100% sure check to guarantee a thread exits other than
the one i use above?
note:
the outer thread is running on a remote host, and the inner threads
are running locally. here are the details:
public class BB implements Runnable, FinInterface {
public void run() {
// do some work on the remote machine
private void startResultsHandler(OisXoos oisX) {
ResultHandler rh = new ResultHandler(oisX);
rh.start();
public void startDataProxy(OisXoos oisX, String query) {
DataProxy dp = new DataProxy(oisX, query);
dp.start();
public class ResultsHandler extends Thread {
// runs locally; waits for results from servers
public void run() {
ObjectInputStream ois = new ObjectInputStream(oisX.input);
Set result = (Set) ois.readObject();
} // ____ class :: _ ResultsHandler _ :: class ____
public class DataProxy extends Thread {
// runs locally; performs db queries on behalf of servers
public void run() {
ObjectOutputStream oos = new ObjectOutputStream(oisX.output);
while(moreData) {
.... // sql queries
oos.writeObject(data);
StartResultsHandler(oisX);
} // _____ class :: _ DataProxy _ :: class _____
}now, the BB class is not started locally.
the inner threads are started locally to both service data requests
by the BB thread as well as wait for its results.
(_) so, maybe the inner threads cannot exit (but they sure look
like they exit) until their parent BB thread exits.
(_) yet, those inner threads have no knowledge that the BB
thread is running.
externalizing those inner thread classes will put 2-weeks of work
in the dust bin. i want to keep them internal.
thanks.
here this piece of code that controls everything:
while(moreData) {
FinObjects finObj = new BB();
String symb = (String) data_ois.readObject();
OisXoos oisX = RSAdmin.getServer();
oisX.xoos.writeObject(finObj);
finObj.startDataProxy(finObj, oisX, symb);
} -
Passing Inner class name as parameter
Hi,
How i can pass inner class name as parameter which is used to create object of inner class in the receiving method (class.formane(className))
Hope somebody can help me.
Thanks in advance.
PremNo, because an inner class can never have a constructor that doesn't take any arguments.
Without going through reflection, you always need an instance of the outer class to instantiate the inner class. Internally this instance is passed as a parameter to the inner class's constructor. So to create an instance of an inner class through reflection you need to get the appropriate constructor and call its newInstance method. Here's a complete example:import java.lang.reflect.Constructor;
class Outer {
class Inner {
public static void main(String[] args) throws Exception{
Class c = Class.forName("Outer$Inner");
Constructor cnstrctr = c.getDeclaredConstructor(new Class[] {Outer.class});
Outer o = new Outer();
Inner i = (Inner) cnstrctr.newInstance(new Object[]{o});
System.out.println(i);
} -
How to call inner class method in one java file from another java file?
hello guyz, i m tryin to access an inner class method defined in one class from another class... i m posting the code too wit error. plz help me out.
// test1.java
public class test1
public test1()
test t = new test();
public class test
test()
public int geti()
int i=10;
return i;
// test2.java
class test2
public static void main(String[] args)
test1 t1 = new test1();
System.out.println(t1.t.i);
i m getting error as
test2.java:7: cannot resolve symbol
symbol : variable t
location: class test1
System.out.println(t1.t.geti());
^There are various ways to define and use nested classes. Here is a common pattern. The inner class is private but implements an interface visible to the client. The enclosing class provides a factory method to create instances of the inner class.
interface I {
void method();
class Outer {
private String name;
public Outer(String name) {
this.name = name;
public I createInner() {
return new Inner();
private class Inner implements I {
public void method() {
System.out.format("Enclosing object's name is %s%n", name);
public class Demo {
public static void main(String[] args) {
Outer outer = new Outer("Otto");
I junior = outer.createInner();
junior.method();
} -
How to access var in outter class inside inner class
I've problem with this, how to access var number1 and number2 at outter class inside inner class? what statement do i have to use to access it ? i tried with " int number1 = Kalkulator1.this.number1; " but there no value at class option var y when the program was running...
import java.io.*;
public class Kalkulator1{
int number1,number2,x;
/* The short way to create instance object for input console*/
private static BufferedReader stdin =
new BufferedReader( new InputStreamReader( System.in ) );
public static void main(String[] args)throws IOException {
System.out.println("---------------------------------------");
System.out.println("Kalkulator Sayur by Cumi ");
System.out.println("---------------------------------------");
System.out.println("Tentukan jenis operasi bilangan [0-4] ");
System.out.println(" 1. Penjumlahan ");
System.out.println(" 2. Pengurangan ");
System.out.println(" 3. Perkalian ");
System.out.println(" 4. Pembagian ");
System.out.println("---------------------------------------");
System.out.print(" Masukan jenis operasi : ");
String ops = stdin.readLine();
int numberops = Integer.parseInt( ops );
System.out.print("Masukan Bilangan ke-1 : ");
String input1 = stdin.readLine();
int number1 = Integer.parseInt( input1 );
System.out.print("Masukan Bilangan ke-2 : ");
String input2 = stdin.readLine();
int number2 = Integer.parseInt( input2 );
Kalkulator1 op = new Kalkulator1();
Kalkulator1.option b = op.new option();
b.pilihan(numberops);
System.out.println("Bilangan yang dimasukkan adalah = " + number1 +" dan "+ number2 );
class option{
int x,y;
int number1 = Kalkulator1.this.number1;
int number2 = Kalkulator1.this.number2;
void pilihan(int x) {
if (x == 1)
{System.out.println("Operasi yang digunakan adalah Penjumlahan");
int y = (number1+number2);
System.out.println("Hasil dari operasi adalah = " + y);}
else
{if (x == 2) {System.out.println("Operasi yang digunakan adalah Pengurangan");
int y = (number1-number2);
System.out.println("Hasil dari operasi adalah = " + y);}
else
{if (x == 3) {System.out.println("Operasi yang digunakan adalah Perkalian");
int y = (number1*number2);
System.out.println("Hasil dari operasi adalah = " + y);}
else
{if (x == 4) {System.out.println("Operasi yang digunakan adalah Pembagian ");
int y = (number1/number2);
System.out.println("Hasil dari operasi adalah =" + y);}
else {System.out.println( "Operasi yang digunakan adalah Pembagian ");
}Delete the variables number1 and number2 from your inner class. Your inner class can access the variables in the outer class directly. Unless you need the inner and outer class variables to hold different values then you can give them different names.
In future place code tags around your code to make it retain formatting. Highlight code and click code button. -
How to pass a variable value to an inner class?
Hi there,
Please have a look of the code below. It's a bit long, but my concern is I did have to declare the int "i" variable as static because it is used by an inner class (if "i" is not declare as static, the code cannot be compiled).
Is there a more "clean" way to do the way work without declaring the "i" int as static? (because the scope of this variable is not the whole program).
Thanks for your help.
Denis
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Tools{
static int i;
static void longTask(){
for (Tools.i=0; Tools.i<=100; Tools.i++) {
SwingUtilities.invokeLater( new Runnable(){
public void run(){
myApp.jpb.setValue(Tools.i);//--- static variable i
for (int j=0; j<200; j++)
System.out.println(Tools.i+" - "+j);
class myListener implements ActionListener{
public void actionPerformed(ActionEvent e){
Thread t = new Thread() {
public void run(){
Tools.longTask();
t.start();
public class myApp {
static JProgressBar jpb;
public static void main(String[] args) {
JFrame frame = new JFrame();
JPanel panel = new JPanel(new FlowLayout());
jpb = new JProgressBar();
jpb.setValue(0);
jpb.setStringPainted(true);
JButton button = new JButton("go");
button.addActionListener(new myListener());
panel.add(jpb);
panel.add(button);
frame.getContentPane().add( panel, BorderLayout.CENTER);
frame.setVisible(true);
frame.pack();
}Without compiling it, writing it in notepad, it would be something like this. You should also wonder if this longTask has to be static by the way. But I think this demonstrates the inner class stuff. You can also look in the tutorial on this site: http://java.sun.com/docs/books/tutorial/essential/threads/timer.html
class Tools{
static int i;
static void longTask(){
for (Tools.i=0; Tools.i<=100; Tools.i++) {
SwingUtilities.invokeLater( new Innerclass(i));
for (int j=0; j<200; j++) {
System.out.println(Tools.i+" - "+j);
Class Innerclass implements Runnable(){
int i;
public Innerclass(int i) {
this.i = i;
public void run(){
myApp.jpb.setValue(Tools.i);//--- static variable i
} -
Trying to use super class's methods from an anonymous inner class
Hi all,
I have one class with some methods, and a second class which inherits from the first. The second class contains a method which starts up a thread, which is an anonymous inner class. Inside this inner class, I want to call a method from my first class. How can I do this?
If I just call the method, it will use the second class's version of the method. However, if I use "super," it will try to find that method in the Thread class (it's own super class) and complain.
Any suggestions?
Code:
public class TopClass
public void doSomething(){
// do something
=============================
public class LowerClass extends TopClass
// overrides TopClass's doSomething.
public void doSomething(){
// do something
public void testThread(){
Thread t = new Thread(){
public void run(){
doSomething(); //fine
super.doSomething(); //WRONG: searches class Thread for doSomething...
t.start();
}Classes frequently call the un-overridden versions of methods from their superclasses. That's that the super keyword is for, if I'm not mistaken.You're not mistaken about the keyword, but you're not calling the superclass method from a subclass. Your anonymous inner class is not a subtype of TopLevel. It's a subtype of Thread.
Here it is no different, except that I happen to be in a thread at the time.It's vastly different, since you're attempting to call the method from an unrelated class; i.e., Thread.
I could also be in a button's action listener, for example. It seems natural to me that if I can do it in a method, I should be able to do it within an anonymous inner class which is inside a method.If you were in an button's action listener and needed to call a superclass' implementation of a method overridden in the button, I'd have the same questions about your design. It seems smelly to me.
~ -
Null pointer exception with inner class
Hi everyone,
I've written an applet that is an animation of a wheel turning. The animation is drawn on a customised JPanel which is an inner class called animateArea. The main class is called Rotary. It runs fine when I run it from JBuilder in the Applet Viewer. However when I try to open the html in internet explorer it gives me null pointer exceptions like the following:
java.lang.NullPointerException
at sun.java2d.SunGraphics2D.drawImage(SunGraphics2D.java:2761)
at sun.java2d.SunGraphics2D.drawImage(SunGraphics2D.java:2722)
at Rotary$animateArea.paintComponent(Rotary.java:251)
at javax.swing.JComponent.paint(JComponent.java:808)
at javax.swing.JComponent.paintWithOffscreenBuffer(JComponent.java:4771)
at javax.swing.JComponent.paintDoubleBuffered(JComponent.java:4724)
at javax.swing.JComponent._paintImmediately(JComponent.java:4668)
at javax.swing.JComponent.paintImmediately(JComponent.java:4477)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:410)
at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:117)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:178)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:448)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:197)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:144)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:136)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:99)
Do inner classes have to be compiled seperately or anything?
Thanks a million for you time,
CurtinRI think that I am using the Java plugin ( Its a computer in college so I'm not certain but I just tried running an applet from the Swing tutorial and it worked)
Its an image of a rotating wheel and in each sector of the wheel is the name of a person - when you click on the sector it goes red and the email window should come up (that doesn't work yet though). The stop and play buttons stop or start the animation. It is started by default.
This is the code for the applet:
import java.applet.*;
import javax.swing.JApplet;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.awt.geom.*;
import javax.swing.*;
import java.awt.image.*;
import java.util.StringTokenizer;
import java.net.*;
public class Rotary extends JApplet implements ActionListener, MouseListener
public boolean rotating;
private Timer timer;
private int delay = 1000;
private AffineTransform transform;
private JTextArea txtTest; //temp
private Container c;
private animateArea wheelPanel;
private JButton btPlay, btStop;
private BoxLayout layout;
private JPanel btPanel;
public Image wheel;
public int currentSector;
public String members[];
public int [][]coordsX, coordsY; //stores sector no. and x or y coordinates for that point
final int TOTAL_SECTORS= 48;
//creates polygon array - each polygon represents a sector on wheel
public Polygon polySector1,polySector2,polySector3, polySector4, polySector5,polySector6,polySector7,polySector8,polySector9,polySector10,
polySector11,polySector12,polySector13,polySector14,polySector15,polySector16,polySector17,polySector18,polySector19,polySector20,
polySector21,polySector22,polySector23,polySector24,polySector25,polySector26,polySector27,polySector28,polySector29,polySector30,
polySector31,polySector32,polySector33,polySector34,polySector35,polySector36,polySector37,polySector38,polySector39,polySector40,
polySector41,polySector42,polySector43,polySector44,polySector45,polySector46,polySector47,polySector48;
public Polygon polySectors[]={polySector1,polySector2,polySector3, polySector4, polySector5,polySector6,polySector7,polySector8,polySector9,polySector10,
polySector11,polySector12,polySector13,polySector14,polySector15,polySector16,polySector17,polySector18,polySector19,polySector20,
polySector21,polySector22,polySector23,polySector24,polySector25,polySector26,polySector27,polySector28,polySector29,polySector30,
polySector31,polySector32,polySector33,polySector34,polySector35,polySector36,polySector37,polySector38,polySector39,polySector40,
polySector41,polySector42,polySector43,polySector44,polySector45,polySector46,polySector47,polySector48};
public void init()
members = new String[TOTAL_SECTORS];
coordsX= new int[TOTAL_SECTORS][4];
coordsY= new int[TOTAL_SECTORS][4];
currentSector = -1;
rotating = true;
transform = new AffineTransform();
//***********************************Create GUI**************************
wheelPanel = new animateArea(); //create a canvas where the animation will be displayed
wheelPanel.setSize(600,580);
wheelPanel.setBackground(Color.yellow);
btPanel = new JPanel(); //create a panel for the buttons
btPanel.setLayout(new BoxLayout(btPanel,BoxLayout.Y_AXIS));
btPanel.setBackground(Color.blue);
btPanel.setMaximumSize(new Dimension(30,580));
btPanel.setMinimumSize(new Dimension(30,580));
btPlay = new JButton("Play");
btStop = new JButton("Stop");
//txtTest = new JTextArea(5,5); //temp
btPanel.add(btPlay);
btPanel.add(btStop);
// btPanel.add(txtTest); //temp
c = getContentPane();
layout = new BoxLayout(c,layout.X_AXIS);
c.setLayout(layout);
c.add(wheelPanel); //add panel and animate canvas to the applet
c.add(btPanel);
wheel = getImage(getDocumentBase(),"rotary2.gif");
getParameters();
for(int k = 0; k <TOTAL_SECTORS; k++)
polySectors[k] = new Polygon();
for(int n= 0; n<4; n++)
polySectors[k].addPoint(coordsX[k][n],coordsY[k][n]);
btPlay.addActionListener(this);
btStop.addActionListener(this);
wheelPanel.addMouseListener(this);
startAnimation();
public void mouseClicked(MouseEvent e)
if (rotating == false) //user can only hightlight a sector when wheel is not rotating
for(int h= 0; h<TOTAL_SECTORS; h++)
if(polySectors[h].contains(e.getX(),e.getY()))
currentSector = h;
wheelPanel.repaint();
email();
public void mouseExited(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
public void mouseReleased(MouseEvent e){}
public void mousePressed(MouseEvent e){}
public void email()
try
URL rotaryMail = new URL("mailto:[email protected]");
getAppletContext().showDocument(rotaryMail);
catch(MalformedURLException mue)
System.out.println("bad url!");
public void getParameters()
StringTokenizer stSector;
String parCoords;
for(int i = 0; i <TOTAL_SECTORS; i++)
{ //put member names in applet parameter list into an array
members[i] = getParameter("member"+i);
//separate coordinate string and store coordinates in 2 arrays
parCoords=getParameter("sector"+i);
stSector = new StringTokenizer(parCoords, ",");
for(int j = 0; j<4; j++)
coordsX[i][j] = Integer.parseInt(stSector.nextToken());
coordsY[i][j] = Integer.parseInt(stSector.nextToken());
public void actionPerformed(ActionEvent e)
wheelPanel.repaint(); //repaint when timer event occurs
if (e.getActionCommand()=="Stop")
stopAnimation();
else if(e.getActionCommand()=="Play")
startAnimation();
public void startAnimation()
if(timer == null)
timer = new Timer(delay,this);
timer.start();
else if(!timer.isRunning())
timer.restart();
Thanks so much for your help! -
Calling functions of the inner class in .java code file
Hello,
I created a .java code file in Visual J#.Net and converted it into
the application by adding the "public static void main(String args[])"
function.
I have created the two classes one extends from Applet, and the other
extends from Frame. The class which I inherited from the Frame class becomes
the inner class of the class extended from the Applet. Now How do I
call the functions of the class extended from Frame class - MenuBarFrame
class. the outline code is
public class menu_show extends Applet
------init , paint action function---------
public class MenuBarFrame extends Frame
paint,action function for Menu
public static void main(String args[])
applet class instance is created
instance of frame is created
Menu , MenuBar, MenuItem instance is created
and all these objects added
I have Created MenuBarFrame class instance as
Object x= new menu_show().new MenuBarFrame
????? How to call the functions such as action of MenuBarFrame class - what
should be its parameters??????
}Here's how I would do it:
interface Operation {
public int op(int y);
class X {
private int x;
public X(int x) {
this.x = x;
private class Y implements Operation {
public int op(int y) {
return x+y;
public Operation createOperation() {
return new Y();
public static void main(String[] args) {
X app = new X(17);
Operation f = app.createOperation();
System.out.println(f.op(-11));
}Your code, however, has some serious "issues". You typically don't
instantiate an applet class -- that's the job of the applet viewer or Java plugin
your browser is using. If you instantiate the applet directly, you're going
to have to supply it an AppletStub. Do you really want to go that way?
Again, use an applet viewer or browser, or better yet, why write applets at all? -
Java Inner classes within the Threading paradigm
Hi all.
Im familiar with static nested classes, method local classes, inner classes and anonymous classes.
But what I am a little perplexed by, is when exactly to use inner classes or static nested classes? (forgetting anonymous classes and method local classes).
I read this article (http://www.javaworld.com/javaworld/javaqa/2000-03/02-qa-innerclass.html) and the first point makes for a good argument, but why nest the class? Why not define it as an external class?
Also you typically find nested classes within the Threading paradigm, but why?
I typically would create a top level class (non nested) that would implement the Runnable interface, override run() and then
use this class when constructing a new Thread.
Any clarification would be greatly received.
Thanks and Happy Friday.Boeing-737 wrote:
I read this article (http://www.javaworld.com/javaworld/javaqa/2000-03/02-qa-innerclass.html) and the first point makes for a good argument, but why nest the class? Why not define it as an external class?
I was going to provide some reasons, but when I read the article I found they were already there. Following the DRY principle I'm going to let the article speak for itself.
Also you typically find nested classes within the Threading paradigm, but why?No, I don't. If that's where you typically find them then you haven't had a varied experience.
I typically would create a top level class (non nested) that would implement the Runnable interface, override run() and then
use this class when constructing a new Thread.So carry on doing that, if it works for you.
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