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)
发表评论 取消回复