我想把自己寫的程序實現為Eclipse插件，
當運行選擇run->org.eclipse.ui.ide.workbench是可以正常運行
但當我我把項目打包放到了plugins下包名字為helloworld.jar
運行的時候就遇到錯誤了，請高手指點，這個問題該怎么解決。謝謝

下面是XML文件

*********************************************************************
<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.0"?>
<plugin
 id="com.yangfei.examples.helloworld"
 name="Hello World Plugin"
 version="1.0.0">
 <requires>
  <import plugin="org.eclipse.ui" />
 </requires>
 <runtime>
  <library name="helloworld.jar" />
 </runtime>
 <extension point="org.eclipse.ui.views">
  <category id="com.yangfei.examples.helloworld.hello" name="Hello" />
  <view id="com.yangfei.examples.helloworld.HelloWorldView"
  name="Hello Greetings"
  category="com.yangfei.examples.helloworld.hello"
  class="com.yangfei.examples.helloworld.HelloWorldView" />
 </extension>
</plugin>
*********************************************************************
##############################################################

這斷HelloWorldView.java的代碼

package com.yangfei.examples.helloworld;

import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.SWT;
import org.eclipse.ui.part.ViewPart;

public class HelloWorldView extends ViewPart {
 Label label;
 public HelloWorldView() {
 }

 public void createPartControl(Composite parent) {
  label = new Label(parent, SWT.WRAP);
  label.setText("Hello World");
 }
 public void setFocus() {
 }

}
##############################################################

windows->show  View->other->Hello->Hello Greetings 時就遇到了錯誤
錯誤信息如下：
java.lang.ClassNotFoundException: com.yangfei.examples.helloworld.HelloWorldView
 at org.eclipse.osgi.framework.internal.core.BundleLoader.findClass(BundleLoader.java:403)
 at org.eclipse.osgi.framework.internal.core.BundleLoader.findClass(BundleLoader.java:350)
 at org.eclipse.osgi.framework.adaptor.core.AbstractClassLoader.loadClass(AbstractClassLoader.java:78)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
 at org.eclipse.osgi.framework.internal.core.BundleLoader.loadClass(BundleLoader.java:275)
 at org.eclipse.osgi.framework.internal.core.BundleHost.loadClass(BundleHost.java:227)
 at org.eclipse.osgi.framework.internal.core.AbstractBundle.loadClass(AbstractBundle.java:1259)
 at org.eclipse.core.internal.registry.ConfigurationElement.createExecutableExtension(ConfigurationElement.java:152)
 at org.eclipse.core.internal.registry.ConfigurationElement.createExecutableExtension(ConfigurationElement.java:142)
 at org.eclipse.core.internal.registry.ConfigurationElement.createExecutableExtension(ConfigurationElement.java:129)
 at org.eclipse.core.internal.registry.ConfigurationElementHandle.createExecutableExtension(ConfigurationElementHandle.java:48)
 at org.eclipse.ui.internal.WorkbenchPlugin$1.run(WorkbenchPlugin.java:240)
 at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:69)
 at org.eclipse.ui.internal.WorkbenchPlugin.createExtension(WorkbenchPlugin.java:236)
 at org.eclipse.ui.internal.registry.ViewDescriptor.createView(ViewDescriptor.java:99)
 at org.eclipse.ui.internal.ViewReference.createPartHelper(ViewReference.java:267)
 at org.eclipse.ui.internal.ViewReference.createPart(ViewReference.java:180)
 at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:552)
 at org.eclipse.ui.internal.PartPane.setVisible(PartPane.java:283)
 at org.eclipse.ui.internal.ViewPane.setVisible(ViewPane.java:512)
 at org.eclipse.ui.internal.presentations.PresentablePart.setVisible(PresentablePart.java:126)
 at org.eclipse.ui.internal.presentations.util.PresentablePartFolder.select(PresentablePartFolder.java:268)
 at org.eclipse.ui.internal.presentations.util.LeftToRightTabOrder.select(LeftToRightTabOrder.java:65)
 at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation.selectPart(TabbedStackPresentation.java:391)
 at org.eclipse.ui.internal.PartStack.refreshPresentationSelection(PartStack.java:1102)
 at org.eclipse.ui.internal.PartStack.createControl(PartStack.java:591)
 at org.eclipse.ui.internal.PartStack.createControl(PartStack.java:528)
 at org.eclipse.ui.internal.PartSashContainer.createControl(PartSashContainer.java:485)
 at org.eclipse.ui.internal.PerspectiveHelper.activate(PerspectiveHelper.java:230)
 at org.eclipse.ui.internal.Perspective.onActivate(Perspective.java:813)
 at org.eclipse.ui.internal.WorkbenchPage.onActivate(WorkbenchPage.java:2165)
 at org.eclipse.ui.internal.WorkbenchWindow$5.run(WorkbenchWindow.java:2356)
 at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:69)
 at org.eclipse.ui.internal.WorkbenchWindow.setActivePage(WorkbenchWindow.java:2338)
 at org.eclipse.ui.internal.WorkbenchWindow.restoreState(WorkbenchWindow.java:1861)
 at org.eclipse.ui.internal.Workbench.doRestoreState(Workbench.java:2566)
 at org.eclipse.ui.internal.Workbench.access$14(Workbench.java:2515)
 at org.eclipse.ui.internal.Workbench$19.run(Workbench.java:1514)
 at org.eclipse.ui.internal.Workbench$16.run(Workbench.java:1263)
 at org.eclipse.jface.operation.ModalContext.runInCurrentThread(ModalContext.java:346)
 at org.eclipse.jface.operation.ModalContext.run(ModalContext.java:291)
 at org.eclipse.jface.dialogs.ProgressMonitorDialog.run(ProgressMonitorDialog.java:447)
 at org.eclipse.ui.internal.Workbench.runStartupWithProgress(Workbench.java:1258)
 at org.eclipse.ui.internal.Workbench.restoreState(Workbench.java:1512)
 at org.eclipse.ui.internal.Workbench.access$12(Workbench.java:1491)
 at org.eclipse.ui.internal.Workbench$17.run(Workbench.java:1374)
 at org.eclipse.core.internal.runtime.InternalPlatform.run(InternalPlatform.java:1044)
 at org.eclipse.core.runtime.Platform.run(Platform.java:783)
 at org.eclipse.ui.internal.Workbench.restoreState(Workbench.java:1318)
 at org.eclipse.ui.internal.WorkbenchConfigurer.restoreState(WorkbenchConfigurer.java:183)
 at org.eclipse.ui.application.WorkbenchAdvisor.openWindows(WorkbenchAdvisor.java:700)
 at org.eclipse.ui.internal.Workbench.init(Workbench.java:1034)
 at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:1636)
 at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:367)
 at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:143)
 at org.eclipse.ui.internal.ide.IDEApplication.run(IDEApplication.java:103)
 at org.eclipse.core.internal.runtime.PlatformActivator$1.run(PlatformActivator.java:226)
 at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:376)
 at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:163)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:585)
 at org.eclipse.core.launcher.Main.invokeFramework(Main.java:334)
 at org.eclipse.core.launcher.Main.basicRun(Main.java:278)
 at org.eclipse.core.launcher.Main.run(Main.java:973)
 at org.eclipse.core.launcher.Main.main(Main.java:948)