ant Could not find Hello. Make sure you have it in your classpath

 [java] Could not find Hello. Make sure you have it in your classpath
     [java]  at org.apache.tools.ant.taskdefs.ExecuteJava.execute(ExecuteJava.java:140)
     [java]  at org.apache.tools.ant.taskdefs.Java.run(Java.java:832)
     [java]  at org.apache.tools.ant.taskdefs.Java.executeJava(Java.java:226)
     [java]  at org.apache.tools.ant.taskdefs.Java.executeJava(Java.java:135)
     [java]  at org.apache.tools.ant.taskdefs.Java.execute(Java.java:108)
     [java]  at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:293)
     [java]  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     [java]  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
     [java]  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
     [java]  at java.lang.reflect.Method.invoke(Method.java:498)
     [java]  at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
     [java]  at org.apache.tools.ant.Task.perform(Task.java:352)
     [java]  at org.apache.tools.ant.Target.execute(Target.java:437)
     [java]  at org.apache.tools.ant.Target.performTasks(Target.java:458)
     [java]  at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1406)
     [java]  at org.apache.tools.ant.Project.executeTarget(Project.java:1377)
     [java]  at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
     [java]  at org.eclipse.ant.internal.launching.remote.EclipseDefaultExecutor.executeTargets(EclipseDefaultExecutor.java:36)
     [java]  at org.apache.tools.ant.Project.executeTargets(Project.java:1261)
     [java]  at org.eclipse.ant.internal.launching.remote.InternalAntRunner.run(InternalAntRunner.java:460)
     [java]  at org.eclipse.ant.internal.launching.remote.InternalAntRunner.main(InternalAntRunner.java:142)
     [java] Java Result: -1

解决方式：
 
           //这个写类的全路径