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java中int初始化可以为0,但不能为NULL问题
tezhongbing · 204浏览 · 发布于2023-02-28 +关注

这篇文章主要介绍了java中int初始化可以为0,但不能为NULL问题,具有很好的参考价值,希望对大家有所帮助。如有错误或未考虑完全的地方,望不吝赐教



int初始化可以为0,但不能为NULL

今天在制作网页的时候,出现一个空指针错误,但是找了半天没有发现,后来发现是int 赋值的时候变成了空值:

要进行判断后赋值

if(aLikesCount.getLikesNumber()!=null){ //int 不能为NULL
 LikesCountNumber=aLikesCount.getLikesNumber();
}
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.index_jsp._jspService(index_jsp.java:803)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter
(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter
(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter
(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter
(ApplicationFilterChain.java:206)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter
(StrutsPrepareAndExecuteFilter.java:96)
at struts2.action.MyEditorStrutsFilter.doFilter(MyEditorStrutsFilter.java:23)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter
(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter
(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke
(ApplicationDispatcher.java:719)
at org.apache.catalina.core.ApplicationDispatcher.processRequest
(ApplicationDispatcher.java:465)
at org.apache.catalina.core.ApplicationDispatcher.doForward
(ApplicationDispatcher.java:390)
at org.apache.catalina.core.ApplicationDispatcher.forward
(ApplicationDispatcher.java:317)
at org.apache.struts2.dispatcher.ServletDispatcherResult.doExecute
(ServletDispatcherResult.java:164)
at org.apache.struts2.dispatcher.StrutsResultSupport.execute
(StrutsResultSupport.java:191)
at com.opensymphony.xwork2.DefaultActionInvocation.executeResult
(DefaultActionInvocation.java:369)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:273)
at org.apache.struts2.interceptor.DeprecationInterceptor.intercept
(DeprecationInterceptor.java:41)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept
(DebuggingInterceptor.java:256)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept
(DefaultWorkflowInterceptor.java:167)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept
(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept
(ValidationInterceptor.java:265)
at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.
doIntercept(AnnotationValidationInterceptor.java:76)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept
(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept
(ConversionErrorInterceptor.java:138)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept
(ParametersInterceptor.java:229)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept
(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept
(ParametersInterceptor.java:229)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept
(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept
(StaticParametersInterceptor.java:191)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at org.apache.struts2.interceptor.MultiselectInterceptor.intercept
(MultiselectInterceptor.java:73)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at org.apache.struts2.interceptor.DateTextFieldInterceptor.intercept
(DateTextFieldInterceptor.java:125)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at org.apache.struts2.interceptor.CheckboxInterceptor.intercept
(CheckboxInterceptor.java:91)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at org.apache.struts2.interceptor.FileUploadInterceptor.intercept
(FileUploadInterceptor.java:253)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept
(ModelDrivenInterceptor.java:100)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept
(ScopedModelDrivenInterceptor.java:141)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept
(ChainingInterceptor.java:145)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept
(PrepareInterceptor.java:171)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept
(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept
(I18nInterceptor.java:139)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept
(ServletConfigInterceptor.java:164)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept
(AliasInterceptor.java:193)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept
(ExceptionMappingInterceptor.java:189)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke
(DefaultActionInvocation.java:244)
at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:564)
at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction
(ExecuteOperations.java:81)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter
(StrutsPrepareAndExecuteFilter.java:99)
at struts2.action.MyEditorStrutsFilter.doFilter(MyEditorStrutsFilter.java:23)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter
(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter
(ApplicationFilterChain.java:206)
at org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal
(OpenSessionInViewFilter.java:151)
at org.springframework.web.filter.OncePerRequestFilter.doFilter
(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter
(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter
(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke
(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke
(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke
(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke
(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke
(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:521)
at org.apache.coyote.http11.AbstractHttp11Processor.process
(AbstractHttp11Processor.java:1096)
at org.apache.coyote.AbstractProtocolA b s t r a c t C o n n e c t i o n H a n d l e r
 . p r o c e s s ( A b s t r a c t P r o t o c o l . j a v a : 674 ) a t o r g .
  a p a c h e . t o m c a t . u t i l . n e t . N i o E n d p o i n t 
  AbstractConnectionHandler.process(AbstractProtocol.java:674) at org.apache.
  tomcat.util.net.NioEndpointAbstractConnectionHandler.process
  (AbstractProtocol.java:674)atorg.apache.tomcat.util.net.NioEndpointSocketProcessor.
  doRun(NioEndpoint.java:1500)
at org.apache.tomcat.util.net.NioEndpointS o c k e t P r o c e s s o r . r u n 
( N i o E n d p o i n t . j a v a : 1456 ) a t j a v a . u t i l . c o n c u r r e n t 
. T h r e a d P o o l E x e c u t o r . r u n W o r k e r 
( U n k n o w n S o u r c e ) a t j a v a . u t i l . c o n c u r r e n t
 . T h r e a d P o o l E x e c u t o r SocketProcessor.run(NioEndpoint.java:1456) 
 at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
  at java.util.concurrent.ThreadPoolExecutorSocketProcessor.run(NioEndpoint.java:1456)
  atjava.util.concurrent.ThreadPoolExecutor.runWorker(UnknownSource)
  atjava.util.concurrent.ThreadPoolExecutorWorker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)


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