Why wait() is there in Object class why not in Thread class

why wait() is there in Object class why not in Thread class .
while we use wait() in the case of thread environment?
If there is any situation where we use it without using threads please mention with example. or link to that example..

839091 wrote:
The question still remain un-answered as the answers provided are not clear. Can anybody explain why wait(), notify() methods are available in Object class and not thread?What part of the answers given did you not understand?
Have you even tried writing any code that uses wait/notify and thought about how you'd write the same code if they existed only on Thread rather than on Object?
Have you studied the basics of Java's multithreading?
Do you know what a lock is?
Do you know what the synchronized keyword does?
Do you understand the relationship between synchronized and wait/notify?
If you can answer yes to these questions, then the reason that wait/notify exist on Object should be obvious. So, which of the above are "no"?

Similar Messages

Error : the class does not match the class of the persisted object

Hi I am new to Java.. I got an exception "the class does not match the class of the persisted object for cl = java.util.Vector : __SUID = -2767605614048989439, getSUID(cl) = 1".. What it implies? I got Serialized stream and Object from Web Server.. How to resolve this Exception? I nead to Deserialize this stream...

ArulPrabhu wrote:
Friend... I agree with u... Every thing Ok... I am not having the option to make change on the server side... I call a webrequest for the URI - "http://www.nseindia.com/chartdata?mkttype=N&series=EQ&symbol=RPOWER&charttype=ONLINE_STOCK".. From that i got response as Serialized Object Stream... Which is the data made available to all through their applet "Chart".. But i need it for my Custom Project.. I know the Structure of class they have serialized... Is their any chance to parce Data from that Stream..
Three words.
You are doomed.
Whatever you end up doing will not be serialization. It will be reverse engineering of a old (dead) format that could go all pear shaped on you when you least expect it. One of the worst problems in using a solution where you reverse engineer, try and guess hackery your way through a proprietary semi (or totally) undocumented format is that it is really impossible to test your code with any degree of certainty. Does your code actually work? Or does it only work because you haven't seen some totally unexpected (but legal for the format) format yet?
Get the producer to produce XML instead of "serialized" data. This is a much better route for you to go down.
If you decide to keep on your path then grab a DataInputStream and go somewhere else because you'll have to figure out the format of another languages serialized data on a place that isn't this site.

Accessing data in a class when not in the class library

Spoiler (Highlight to read)
Hi,
I'm fairly new to labview classes and am wondering if it is possible to make public or read the value coming from a lvclass control.
If I highlight the control all the values are listed as private and I can't unbundle the class, of course once I make a vi a member of the lvclass I can unbundle the class. However there are two elements that I want o be globally available, is this possible?
Sean

You need to select your class, not the ctl.
This is the same thing as making a member vi for the class, it's just a shortcut for making a .vi that can output the private date.
( The way LabVIEW has implemented the OOP, all class attributes are private. And there are no way to make them public or protected. The only way to access the data from outside is by making a Accessor. )
Here are some reading: http://zone.ni.com/devzone/cda/tut/p/id/3574

BOXIR2: Object name not prefixed with class

While creating Webintelligence report from a universe having more than one Dimension object with same name in different classes, the Object name is not prefixed with Class Name.
1. The issue occurs after migration to XIR2 Webintelligence.
2. 6.5 version of WebIntelligence and XI Desktop intelligence is prefixing class name in above scenario.
REPRODUCTION STEPS:
Create a universe with 2 classes (C1 & C2), Create a dimension object D1, D2 under class C1 and D2 & D3 under class C2. Export the universe.
Create a webi report from the published universe, In Java Query panel , Drag all 4 Dimension Objects to Query Filter Section.
Perform the above in Webintelligence of BO 6.5 & BO XI. Note that in BOXI Class name is not prefixed.
Please let me know weather its change in the product or bug.

Yes this is a bug...

"Class Circle not found in TryBouncingBalls" error message. Help !

Dear People,
I have an error message :
"TryBouncingBalls.java": Error : class Circle not found in class stan_bluej_ch5_p135.TryBouncingBalls at line 67, "
Circle circle = new Circle(xPos + 130, 30);
below are the classes TryBouncingBalls, BouncingBall, BallDemo, Canvas
Thank you in advance
Stan
package stan_bluej_ch5_p135;
import java.awt.*;
import java.awt.geom.*;
public class TryBouncingBalls
public static void main(String[] args)
Canvas myCanvas = new Canvas("Creativity at its best");
myCanvas.setVisible(true);
BouncingBall ball = new BouncingBall(50,50,16, Color.red, 500, myCanvas);
BouncingBall ball2 = new BouncingBall(70,80,20, Color.green, 500, myCanvas);
BouncingBall ball3 = new BouncingBall(90,100,16, Color.red, 500, myCanvas);
BouncingBall ball4 = new BouncingBall(30,30,20, Color.green, 500, myCanvas);
ball.draw();
ball2.draw();
ball.draw();
ball2.draw();
// make them bounce
boolean finished = false;
while(!finished) {
myCanvas.wait(50); // small delay
ball.move();
ball2.move();
ball3.move();
ball4.move();
// stop once ball has travelled a certain distance on x axis
if(ball.getXPosition() >= 550 && ball2.getXPosition() >= 550)
finished = true;
myCanvas.setFont(new Font("helvetica", Font.BOLD, 14));
myCanvas.setForegroundColor(Color.red);
myCanvas.drawString("We are having fun, ...\n\n", 20, 30);
myCanvas.wait(1000);
myCanvas.setForegroundColor(Color.black);
myCanvas.drawString("...drawing lines...", 60, 60);
myCanvas.wait(500);
myCanvas.setForegroundColor(Color.gray);
myCanvas.drawLine(200, 20, 300, 50);
myCanvas.wait(500);
myCanvas.setForegroundColor(Color.blue);
myCanvas.drawLine(220, 100, 370, 40);
myCanvas.wait(500);
myCanvas.setForegroundColor(Color.green);
myCanvas.drawLine(290, 10, 320, 120);
myCanvas.wait(1000);
myCanvas.setForegroundColor(Color.gray);
myCanvas.drawString("...and shapes!", 110, 90);
myCanvas.setForegroundColor(Color.red);
myCanvas.drawString("to bring to focus creative ideas !", 310, 290);
// the shape to draw and move
int xPos = 10;
Rectangle rect = new Rectangle(xPos + 40, 150, 30, 20);
Rectangle rect2 = new Rectangle(xPos + 80, 120, 50, 25);
Rectangle rect3 = new Rectangle(xPos+ 1200, 180, 30, 30);
Rectangle rect4 = new Rectangle(xPos + 150, 220, 40, 15);
myCanvas.fill(rect);
myCanvas.fill(rect2);
myCanvas.fill(rect3);
myCanvas.fill(rect4);
Circle circle = new Circle(xPos + 130, 30);
// Circle circle2 = new Circle(xPos + 150, 50);
// Circle circle3 = new Circle(xPos + 170, 30);
// Circle circle4 = new Circle(xPos + 200, 40);
// myCanvas.fill(circle);
// myCanvas.fill(circle2);
// myCanvas.fill(circle3);
// myCanvas.fill(circle4);
// move the rectangle and circles across the screen
for(int i = 0; i < 200; i ++) {
myCanvas.fill(rect);
myCanvas.fill(rect2);
myCanvas.fill(rect3);
myCanvas.fill(rect4);
myCanvas.wait(10);
myCanvas.erase(rect);
myCanvas.erase(rect2);
myCanvas.erase(rect3);
myCanvas.erase(rect4);
xPos++;
rect.setLocation(xPos, 150);
rect2.setLocation(xPos, 120);
rect3.setLocation(xPos, 180);
rect4.setLocation(xPos, 220);
// at the end of the move, draw once more so that it remains visible
myCanvas.fill(rect);
myCanvas.fill(rect2);
myCanvas.fill(rect3);
myCanvas.fill(rect4);
package stan_bluej_ch5_p135;
import java.awt.*;
import java.awt.geom.*;
* Class BouncingBall - a graphical ball that observes the effect of gravity. The ball
* has the ability to move. Details of movement are determined by the ball itself. It
* will fall downwards, accelerating with time due to the effect of gravity, and bounce
* upward again when hitting the ground.
* This movement can be initiated by repeated calls to the "move" method.
* @author Bruce Quig
* @author Michael Kolling (mik)
* @author David J. Barnes
* @version 1.1 (23-Jan-2002)
public class BouncingBall
private static final int gravity = 3; // effect of gravity
private int ballDegradation = 2;
private Ellipse2D.Double circle;
private Color color;
private int diameter;
private int xPosition;
private int yPosition;
private final int groundPosition; // y position of ground
private Canvas canvas;
private int ySpeed = 1; // initial downward speed
* Constructor for objects of class BouncingBall
* @param xPos the horizontal coordinate of the ball
* @param yPos the vertical coordinate of the ball
* @param ballDiameter the diameter (in pixels) of the ball
* @param ballColor the color of the ball
* @param groundPos the position of the ground (where the wall will bounce)
* @param drawingCanvas the canvas to draw this ball on
public BouncingBall(int xPos, int yPos, int ballDiameter, Color ballColor,
int groundPos, Canvas drawingCanvas)
xPosition = xPos;
yPosition = yPos;
color = ballColor;
diameter = ballDiameter;
groundPosition = groundPos;
canvas = drawingCanvas;
* Draw this ball at its current position onto the canvas.
public void draw()
canvas.setForegroundColor(color);
canvas.fillCircle(xPosition, yPosition, diameter);
* Erase this ball at its current position.
public void erase()
canvas.eraseCircle(xPosition, yPosition, diameter);
* Move this ball according to its position and speed and redraw.
public void move()
// remove from canvas at the current position
erase();
// compute new position
ySpeed += gravity;
yPosition += ySpeed;
xPosition +=2;
// check if it has hit the ground
if(yPosition >= (groundPosition - diameter) && ySpeed > 0) {
yPosition = (int)(groundPosition - diameter);
ySpeed = -ySpeed + ballDegradation;
// draw again at new position
draw();
* return the horizontal position of this ball
public int getXPosition()
return xPosition;
* return the vertical position of this ball
public int getYPosition()
return yPosition;
package stan_bluej_ch5_p135;
import java.awt.*;
import java.awt.geom.*;
* Class BallDemo - provides two short demonstrations showing how to use the
* Canvas class.
* @author Michael Kolling and David J. Barnes
* @version 1.0 (23-Jan-2002)
public class BallDemo
private Canvas myCanvas;
* Create a BallDemo object. Creates a fresh canvas and makes it visible.
public BallDemo()
myCanvas = new Canvas("Ball Demo", 600, 500);
myCanvas.setVisible(true);
* This method demonstrates some of the drawing operations that are
* available on a Canvas object.
public void drawDemo()
myCanvas.setFont(new Font("helvetica", Font.BOLD, 14));
myCanvas.setForegroundColor(Color.red);
myCanvas.drawString("We can draw text, ...", 20, 30);
myCanvas.wait(1000);
myCanvas.setForegroundColor(Color.black);
myCanvas.drawString("...draw lines...", 60, 60);
myCanvas.wait(500);
myCanvas.setForegroundColor(Color.gray);
myCanvas.drawLine(200, 20, 300, 50);
myCanvas.wait(500);
myCanvas.setForegroundColor(Color.blue);
myCanvas.drawLine(220, 100, 370, 40);
myCanvas.wait(500);
myCanvas.setForegroundColor(Color.green);
myCanvas.drawLine(290, 10, 320, 120);
myCanvas.wait(1000);
myCanvas.setForegroundColor(Color.gray);
myCanvas.drawString("...and shapes!", 110, 90);
myCanvas.setForegroundColor(Color.red);
// the shape to draw and move
int xPos = 10;
Rectangle rect = new Rectangle(xPos, 150, 30, 20);
// move the rectangle across the screen
for(int i = 0; i < 200; i ++) {
myCanvas.fill(rect);
myCanvas.wait(10);
myCanvas.erase(rect);
xPos++;
rect.setLocation(xPos, 150);
// at the end of the move, draw once more so that it remains visible
myCanvas.fill(rect);
* Simulates two bouncing balls
public void bounce()
int ground = 400; // position of the ground line
myCanvas.setVisible(true);
// draw the ground
myCanvas.drawLine(50, ground, 550, ground);
// crate and show the balls
BouncingBall ball = new BouncingBall(50, 50, 16, Color.blue, ground, myCanvas);
ball.draw();
BouncingBall ball2 = new BouncingBall(70, 80, 20, Color.red, ground, myCanvas);
ball2.draw();
// make them bounce
boolean finished = false;
while(!finished) {
myCanvas.wait(50); // small delay
ball.move();
ball2.move();
// stop once ball has travelled a certain distance on x axis
if(ball.getXPosition() >= 550 && ball2.getXPosition() >= 550)
finished = true;
ball.erase();
ball2.erase();
package stan_bluej_ch5_p135;
import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;
* Class Canvas - a class to allow for simple graphical
* drawing on a canvas.
* @author Michael Kolling (mik)
* @author Bruce Quig
* @version 1.8 (23.01.2002)
public class Canvas
private JFrame frame;
private CanvasPane canvas;
private Graphics2D graphic;
private Color backgroundColor;
private Image canvasImage;
* Create a Canvas with default height, width and background color
* (300, 300, white).
* @param title title to appear in Canvas Frame
public Canvas(String title)
this(title, 600, 600, Color.white);
* Create a Canvas with default background color (white).
* @param title title to appear in Canvas Frame
* @param width the desired width for the canvas
* @param height the desired height for the canvas
public Canvas(String title, int width, int height)
this(title, width, height, Color.white);
* Create a Canvas.
* @param title title to appear in Canvas Frame
* @param width the desired width for the canvas
* @param height the desired height for the canvas
* @param bgClour the desired background color of the canvas
public Canvas(String title, int width, int height, Color bgColor)
frame = new JFrame();
canvas = new CanvasPane();
frame.setContentPane(canvas);
frame.setTitle(title);
canvas.setPreferredSize(new Dimension(width, height));
backgroundColor = bgColor;
frame.pack();
* Set the canvas visibility and brings canvas to the front of screen
* when made visible. This method can also be used to bring an already
* visible canvas to the front of other windows.
* @param visible boolean value representing the desired visibility of
* the canvas (true or false)
public void setVisible(boolean visible)
if(graphic == null) {
// first time: instantiate the offscreen image and fill it with
// the background color
Dimension size = canvas.getSize();
canvasImage = canvas.createImage(size.width, size.height);
graphic = (Graphics2D)canvasImage.getGraphics();
graphic.setColor(backgroundColor);
graphic.fillRect(0, 0, size.width, size.height);
graphic.setColor(Color.black);
frame.show();
* Provide information on visibility of the Canvas.
* @return true if canvas is visible, false otherwise
public boolean isVisible()
return frame.isVisible();
* Draw the outline of a given shape onto the canvas.
* @param shape the shape object to be drawn on the canvas
public void draw(Shape shape)
graphic.draw(shape);
canvas.repaint();
* Fill the internal dimensions of a given shape with the current
* foreground color of the canvas.
* @param shape the shape object to be filled
public void fill(Shape shape)
graphic.fill(shape);
canvas.repaint();
* Fill the internal dimensions of the given circle with the current
* foreground color of the canvas.
public void fillCircle(int xPos, int yPos, int diameter)
Ellipse2D.Double circle = new Ellipse2D.Double(xPos, yPos, diameter, diameter);
fill(circle);
* Fill the internal dimensions of the given rectangle with the current
* foreground color of the canvas. This is a convenience method. A similar
* effect can be achieved with the "fill" method.
public void fillRectangle(int xPos, int yPos, int width, int height)
fill(new Rectangle(xPos, yPos, width, height));
* Erase the whole canvas.
public void erase()
Color original = graphic.getColor();
graphic.setColor(backgroundColor);
Dimension size = canvas.getSize();
graphic.fill(new Rectangle(0, 0, size.width, size.height));
graphic.setColor(original);
canvas.repaint();
* Erase the internal dimensions of the given circle. This is a
* convenience method. A similar effect can be achieved with
* the "erase" method.
public void eraseCircle(int xPos, int yPos, int diameter)
Ellipse2D.Double circle = new Ellipse2D.Double(xPos, yPos, diameter, diameter);
erase(circle);
* Erase the internal dimensions of the given rectangle. This is a
* convenience method. A similar effect can be achieved with
* the "erase" method.
public void eraseRectangle(int xPos, int yPos, int width, int height)
erase(new Rectangle(xPos, yPos, width, height));
* Erase a given shape's interior on the screen.
* @param shape the shape object to be erased
public void erase(Shape shape)
Color original = graphic.getColor();
graphic.setColor(backgroundColor);
graphic.fill(shape); // erase by filling background color
graphic.setColor(original);
canvas.repaint();
* Erases a given shape's outline on the screen.
* @param shape the shape object to be erased
public void eraseOutline(Shape shape)
Color original = graphic.getColor();
graphic.setColor(backgroundColor);
graphic.draw(shape); // erase by drawing background color
graphic.setColor(original);
canvas.repaint();
* Draws an image onto the canvas.
* @param image the Image object to be displayed
* @param x x co-ordinate for Image placement
* @param y y co-ordinate for Image placement
* @return returns boolean value representing whether the image was
* completely loaded
public boolean drawImage(Image image, int x, int y)
boolean result = graphic.drawImage(image, x, y, null);
canvas.repaint();
return result;
* Draws a String on the Canvas.
* @param text the String to be displayed
* @param x x co-ordinate for text placement
* @param y y co-ordinate for text placement
public void drawString(String text, int x, int y)
graphic.drawString(text, x, y);
canvas.repaint();
* Erases a String on the Canvas.
* @param text the String to be displayed
* @param x x co-ordinate for text placement
* @param y y co-ordinate for text placement
public void eraseString(String text, int x, int y)
Color original = graphic.getColor();
graphic.setColor(backgroundColor);
graphic.drawString(text, x, y);
graphic.setColor(original);
canvas.repaint();
* Draws a line on the Canvas.
* @param x1 x co-ordinate of start of line
* @param y1 y co-ordinate of start of line
* @param x2 x co-ordinate of end of line
* @param y2 y co-ordinate of end of line
public void drawLine(int x1, int y1, int x2, int y2)
graphic.drawLine(x1, y1, x2, y2);
canvas.repaint();
* Sets the foreground color of the Canvas.
* @param newColor the new color for the foreground of the Canvas
public void setForegroundColor(Color blue)
graphic.setColor(Color.blue);
* Returns the current color of the foreground.
* @return the color of the foreground of the Canvas
public Color getForegroundColor()
return graphic.getColor();
* Sets the background color of the Canvas.
* @param newColor the new color for the background of the Canvas
public void setBackgroundColor(Color newColor)
backgroundColor = newColor;
graphic.setBackground(newColor);
* Returns the current color of the background
* @return the color of the background of the Canvas
public Color getBackgroundColor()
return backgroundColor;
* changes the current Font used on the Canvas
* @param newFont new font to be used for String output
public void setFont(Font newFont)
graphic.setFont(newFont);
* Returns the current font of the canvas.
* @return the font currently in use
public Font getFont()
return graphic.getFont();
* Sets the size of the canvas.
* @param width new width
* @param height new height
public void setSize(int width, int height)
canvas.setPreferredSize(new Dimension(width, height));
Image oldImage = canvasImage;
canvasImage = canvas.createImage(width, height);
graphic = (Graphics2D)canvasImage.getGraphics();
graphic.drawImage(oldImage, 0, 0, null);
frame.pack();
* Returns the size of the canvas.
* @return The current dimension of the canvas
public Dimension getSize()
return canvas.getSize();
* Waits for a specified number of milliseconds before finishing.
* This provides an easy way to specify a small delay which can be
* used when producing animations.
* @param milliseconds the number
public void wait(int milliseconds)
try
Thread.sleep(milliseconds);
catch (InterruptedException e)
// ignoring exception at the moment
* Nested class CanvasPane - the actual canvas component contained in the
* Canvas frame. This is essentially a JPanel with added capability to
* refresh the image drawn on it.
private class CanvasPane extends JPanel
public void paint(Graphics g)
g.drawImage(canvasImage, 0, 0, null);

Dear Miciuli,
I found the definition for the circle in the canvas class and used it to creates circles ! Thank you for jaring my brain into thinking !
Stan
Ellipse2D.Double circle = new Ellipse2D.Double(xPos, 70, 30 , 30);

Problem with Player class: Error: (28) class Player not found

Hi,
I had this error while attempting to use the Player object of media package. I am using JDeveloper 3.2
Error: (28) class Player not found in class lyee.Frame5.
My program code has this shape.
import java.awt.event.*;
import java.applet.*;
import java.net.*;
import java.io.*;
import javax.media.*;
public class Frame5 extends JFrame {
FlowLayout flowLayout = new FlowLayout();
JPanel jPanel1 = new JPanel();
Player lecteur;
Could someone help me finding where the error is exactly. The Player object is in javax.media pakcage, right ? Is there any librarary missing ??
Thank you
Jaouhar

If you haven't done so already, you have to install JMF -- Java Media Framework, which you can download from the Sun website ( http://java.sun.com ). After that, you have to add that library to your project, in your project settings dialog.

What is the impact of creating a thread in a class or outside of the class

Hi Java Experts;
I have 2 code examples on how to create new threads.
The first example instantiates, Starts and Joins the Threads Externally.
The second example Starts and Joins the New Thread Internally.
QUESTIONS:
1. Is it true that creating the thread internally creates 2 new threads instead of just one. Because the instance of Class A is a thread. And when it starts itself that's another thread.
2. Am I correct when I say that the another difference between the two is that in the external one, Class B has to wait before creating new instances since the join method is in its loop. But the advantage of Internally created is that Class B can create can create 100 new threads without having to wait on the join.
are these correct - and is there any other implication of using one versus another.
Scenario 1: Start and Join the New Thread Externally
class A implements Runnable{
public void run(){
public A(){}
public String getMiscProperties(){
   //This Methods must be called Only After this thread returns from the run method
// this is the calling class
class B implements Runnable{
public void run(){
     while(true){
     A p2 = new A();
     Thread t2 = new Thread(p2);
     t2.setDaemon(true);
     t2.start();
     try{
          t2.join();
     }catch(InterruptedException ie){ }
        System.out.println(p2.getMiscProperties());
public B(){}
}Scenario 2: Start and Join the New Thread Internally
class A implements Runnable{
public void run(){
public A(){
     Thread t2 = new Thread(this);
     t2.setDaemon(true);
     t2.start();
     try{
          t2.join();
     }catch(InterruptedException ie){ }
public String getMiscProperties(){
   //This Methods must be called Only After this thread returns from the run method
// this is the calling class
class B implements Runnable{
public void run(){
     while(true){
     A p2 = new A();
        System.out.println(p2.getMiscProperties());
public B(){}

Hi,
1. A thread is created only after you do a
new Thread(..); // (or its subclass)It does not matter whether you do that internally or externally. You do not get a new thread from constructing a class that implements Runnable if this class is not a Thread (or its subclass).
In particular, the line:
A p2 = new A();does not create a new thread by itself. You can verify this by putting
System.out.println(Thread.currentThread().getName());before that line and in the class 'A' constructor.
2. No. Your internally created thread will complete first because it is joined before B.run() gets a chance to create another thread.
If you want to start new threads before other threads complete, you have to do so before the join() method, or you can eliminate join() completely. When you call T.join(), that thread waits for thread T to complete before carrying on.

Is it possible to get the main class name in a Thread context ?

for example, i want to get the main class name (the first entry of the program).
public class Test implements Runnable {
     public Test() {}
     public static void main(String[] args) {
          new Thread(new Test()).start();
     public void run() {
          try {
               //Want to get the main class name (not the current class name)
               throw new Throwable();
          } catch (Throwable e) {
               e.printStackTrace();
}

Acutally, i wanna make clear about the concept of a "Thread"
Is it true that ..
the main() method is a thread , once I create another thread in the program , both of (or all of them) will contains it owns stack exception information ?
My english is poor, please try to understand it. Thx

Weblogic Startup Class does not run as Windows Service

If you know the answer, plase send me an email at [email protected]
I'm running a weblogic startup class that starts a Thread. I need to
run a batch program that should be running as long as WebLogic is
running (to process new orders).
It works fine when I run WebLogic (5.1 SP8) from a script, but causes
problem when I'm running it as a Windows Service. It calls the
startup class, however, the startup class never spawns the Thread
class.
Following is excerpts from different components:
=============================================================
*** weblogic.properties ***
weblogic.system.startupClass.pdfCreatorStart=WebLogicStartupPdfCreator
*** WebLogicStartupPdfCreator.java ***
public class WebLogicStartupPdfCreator implements T3StartupDef {
public String startup(String name, Hashtable args) throws
Exception {
Thread t = new ProductionPdfBatchRunner();
t.start();
return "success";
*** ProductionPdfBatchRunner.java ***
public class ProductionPdfBatchRunner extends Thread {
public void run() {
try {
//work being done here
this.sleep(30000);
catch (InterruptedException ie) {
catch(Exception e) {
e.printStackTrace();
=============================================================
Thanks for any help

Hi,
Ok. Few suggestions.
1. Can you review the SAP note:
552286 Troubleshooting for the SAP Web Dispatcher
2. When you said: "web dispatcher does not get started ", what error you got ? Can you be more details here ?
3. Please check the trace file dev_webdisp" that generated in the work directory. If the log entries is not abvious, increase the trace level to 2 or 3, and reproduce and re-check the trace file.
4. What is the output of the command "sapwebdisp -v"
5. How about sapwebdisp.pfl ? Are those settings correct ?
Hope this helps.
Regards,
Vincent

Why wait and notify kept in object class only

why wait and notify kept in object class only. is it maintain locks while doing wait and notify . please explain internals,

What do you mean in Object class "only"? If they're in Object, then they're in ALL classes.
They're in Object because any Object can serve as a lock.
For details of how to use them, see a Java threading tutorial such as http://java.sun.com/docs/books/tutorial/essential/threads/

Why isn't Java's Object class abstract?

Why isn't java's Object class made as abstract class.

manoj.java wrote:
Why isn't java's Object class made as abstract class.The only good reason I can think of is that, back in the days prior to Java 5 and the incorporation of java.util.concurrent, bare Objects are useful as thread synchronization monitors (wait(), notify(), notifyAll()).
--p

Why do we need to take a lock before invoking wait()/notify() on an Object?

Hi,
Why do we need to take a lock before invoking wait()/notify() on an Object? i know that we shud take otherwise illegalstateexception is thrown.
what is the reason to take a lock bfefore invoking the above methods. why does jvm expects from the programmer?

Please do not crosspost..

Why java is called pure object oriented.

i know that java is called as pure object oriented language.
why it is called so even though it has primitive datatypes and also it doesnot support multiple inheritance completely. it only supports in the case of interfaces but not in the case of classes. then why it is called pure object oriented.

Its because you cannot write an executable java program without creating an object. Well, you can:
public class a
public static void main( String a[] )
}In contrary to C++, there can be no variables or functions in the wild (outside a class).
You can not create an executable java program without creating a class (but not forcibly its instance, an object.)
The "pure object oriented" wording in this sense has not really much importance, it is rather a marketing ploy.

Jar file could not find main class.. I cant see why?

I have read loads of tutorials on this and it should be very straight forward but i STILL cant make a working jar file of my program.. please see if you can see anything wrong with what im doing..
my program is one .java file that compiles perfectly, and is runnable both through eclipse and by using the command prompt.. i made a jar file using both eclipse and the command prompt, and neither worked.. every time i run it by double clicking it i get the error "could not find main class, program will exit". here is the contents of my jar:
CorePackage\IPEmailer.class
CorePackage\IPEmailer$1.class
CorePackage\IPEmailer$SMTPAuthenticator.class
META-INF\MANIFEST.MF
the MANIFEST.MF file contains:
Manifest-Version: 1.0
Class-path: .
Created-By: 1.6.0_02 (Sun Microsystems Inc.)
Main-Class: CorePackage.IPEmailer
(yes there is a blank line at the end)
the class mentioned in 'Main-Class' has a main method that looks like this:
public static void main(String[] args) {
    // TODO Auto-generated method stub
    new IPEmailer();
}the program uses 2 external jar files:
activation.jar
mail.jar
and reads a file called:
ipemailer.ini
and writes a file called:
ip.txt
the program has no GUI and is intended to run 'silently' in the background
please help me understand what is wrong with this

package CorePackage;
import javax.mail.*;
import javax.mail.Authenticator;
import javax.mail.PasswordAuthentication;
import javax.mail.internet.*;
import java.util.*;
import java.io.*;
import java.net.*;
public class IPEmailer implements Runnable{
      * @param args
     String recipientsinput[]={""};
     String subject;
     String body;
     String server;
     String user;
     String pass;
     String from;
     String urlString = "http://www.whatismyip.org";
     String currentIP;
     String ipFromFile;
     boolean webFailed;
     long interval = 900000; //15 mins
     long oldInterval;
     Thread t = new Thread(this);
     public static void main(String[] args) {
          // TODO Auto-generated method stub
          new IPEmailer();
     public IPEmailer(){
                     ..........etccould the problem be that the class is a thread? i cant see why it would be, but ive never made a jar where the main class also 'implements runnable'

Only one public class - why???

Hi
I have come across this statement many places -
"There can be only one Top-Level 'public' class in
a java source file which should have same name as that
of the fore mentioned class."
I know that the compiler searches for the class
with same name as that of the file that is passed to
the compiler.I am also aware that a Java source compiles
smoothly with One or None Top-Level 'public' class,
but I fail to comprehend this -
Why can there be only one TOP-LEVEL 'public' class
in a Java Source file?
The importance of 'TOP-LEVEL' is as important as
any thing else, as you yourself check that a Nested
class within an Enclosing class can be 'public' along
with someother Top-Level 'public' class in the program
compiles smoothly unlike having TWO Top-Level 'public'
classes in same file.
I have found no reason supporting this statement in any
of the refernces I have checked out.Ppl I have asked told
me that it is so coz Java Spec say so.
Is there an better answer to my question?
Thanx in advance, appretiate it.
Regards
Pradeepto

I have found no reason supporting this statement in
in any
of the refernces I have checked out.Ppl I have asked
told
me that it is so coz Java Spec say so.I can tell you that anybody who says its because the Java spec says so, is wrong - the Java spec does not say so.
It is a limitation of Sun's javac compiler, which many other compilers exhibit as well. I don't know the full formal reasoning behind it (and would be interested in knowing if you find a good answer), but I assume it simply has to do with finding classes without having to load everything on your classpath.
Whether other compilers are purposely acting the same way as javac, or whether it is some sort of performance optimisation that most vendors feel is worthwhile, I couldn't say.
I don't see what you're saying about top-level and nested classes. Although you can declare a public nested class inside a non-public top-level class, the nested class is not actually publicly visible, by virue of its enclosing class not being publicly visible.

Why wait() is there in Object class why not in Thread class

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