Question

当我测试eclipse JDT包时，以下代码导致了空指针异常。

parse.findDeclaringNode(method.resolveMethodBinding()).getClass();

奇怪的是以下代码，

System.out.println("Binding start: " + parse.findDeclaringNode(method.resolveMethodBinding()));

打印以下内容：

Binding start: public static int test(){
  return 1;
}

很明显，parse.findDeclaringNode(method.resolveMethodBinding())返回的内容不为空。

然而，尽管打印了一些内容，但是如下所示添加toString（）也会产生空指针异常，这表明打印甚至不会通过＆＃34; toString（）＆＃34;：

parse.findDeclaringNode(method.resolveMethodBinding()).toString();

在我解释代码应该做什么之前，这是运行"parse.findDeclaringNode(method.resolveMethodBinding()).getClass();"的异常的控制台输出：

!ENTRY org.eclipse.ui 4 0 2018-01-23 20:46:17.150
!MESSAGE Unhandled event loop exception
!STACK 0
org.eclipse.e4.core.di.InjectionException: java.lang.NullPointerException
    at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:65)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:305)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:239)
    at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:132)
    at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:152)
    at org.eclipse.core.commands.Command.executeWithChecks(Command.java:494)
    at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:487)
    at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:210)
    at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.executeItem(HandledContributionItem.java:431)
    at org.eclipse.e4.ui.workbench.renderers.swt.AbstractContributionItem.handleWidgetSelection(AbstractContributionItem.java:446)
    at org.eclipse.e4.ui.workbench.renderers.swt.AbstractContributionItem.lambda$2(AbstractContributionItem.java:472)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:86)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4428)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1079)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4238)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3817)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1150)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1039)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:153)
    at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:680)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:594)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:151)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:653)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:590)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1499)
    at org.eclipse.equinox.launcher.Main.main(Main.java:1472)
Caused by: java.lang.NullPointerException
    at de.vogella.jdt.astsimple.handlers.SampleHandler.createAST(SampleHandler.java:89)
    at de.vogella.jdt.astsimple.handlers.SampleHandler.analyseMethods(SampleHandler.java:52)
    at de.vogella.jdt.astsimple.handlers.SampleHandler.execute(SampleHandler.java:37)
    at org.eclipse.ui.internal.handlers.HandlerProxy.execute(HandlerProxy.java:291)
    at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:92)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:55)
    ... 37 more

让我解释一下parse.findDeclaringNode(method.resolveMethodBinding()))是什么。

＆＃34;解析＆＃34;是CompilationUnit和＆＃34;方法＆＃34;是MethodInvocation。 parse.findDeclaringNode(method.resolveMethodBinding())应返回ASTNode。 Eclipse会识别这一点，所以如果我输入该行并在末尾添加句点，它会建议我使用ASTNode的方法。

此外，输入System.out.println(parse.findDeclaringNode(method.resolveMethodBinding()) instanceof String);会让Eclipse抱怨Incompatible conditional operand types ASTNode and String。因此，即使导入的包也建议返回ASTNode。

但是，System.out.println(parse.findDeclaringNode(method.resolveMethodBinding()) instanceof ASTNode);打印错误。

我不知道parse.findDeclaringNode(method.resolveMethodBinding())实际上正在返回什么。

=========== UPDATE ===============

当我做ASTNode test = parse.findDeclaringNode(method.resolveMethodBinding());时发生了奇怪的事情。 Eclipse调试器显示＆＃34; test＆＃34;为null，甚至用test == null进行测试都返回true。

显然parse.findDeclaringNode(method.resolveMethodBinding())会返回可以打印的内容但是当被指定为ASTNode对象时，它会变为空。

为什么＆＃34; a.getClass（）＆＃34; ＆＃34; a＆＃34;会导致空指针异常。可以在控制台打印？

0 个答案: