java语言基础-4异常处理机制

课堂讨论要点

错误异常比如,当系统发现网络意外终止，应把程序挂起，提示用户异常原因，引导用户解决 e.try块中发生异常的语句之后的语句将不再运行。try块中一般放置编程人员认为最可能抛出异常的高危语句，try块中的语句如果抛出了异常，那么该语句之后的语句将不再运行(try块中catchcatch块对异常进行捕获处理，以免造成程序停机。Exceptioncatchcatch模组因代码无法,鱼均可运行，也不怕try途return.try语句运行过程中申请的资源，finally块为此而生。throwthrowsthrow抛出if(b<0thrownewRuntimeException("b不能为负数一个方法的最后部分将用来这个方抛出什么样的异常，以方便调用该方法的方throwsXxxxmethodNamethrows如果一个类中会抛出异常，该异常并不在这个类中获，就必须做好方法的异常一个异常要么获处理，要么被抛出，如被抛出方法，则方法必须异常信息。任何一个方法，将默认在其签名上写上throwsRuntimeException;Inthefollowingcode,whichlineswillbeprintedonthestandardoutput?publicclassTest{publicvoidmethod1(intx)throws{{System.out.println("Checkpoint1");}{}}publicvoidmethod2(intx)throws{if(x<{thrownew}}staticpublicvoidmain(String[]args)throws{Testt=newTest();}}CheckpointCheckpointCheckpointCheckpoint运行时异常(Runtimeextends检查异常(checkedextendsclassApublicvoidprocess(){System.out.print(”A“);}classBextendsApublicvoidprocess()throwsNullPointerExceptionif(true)thrownewNullPointerExceptionpublicstaticvoidmain(String[]args)try{((A)newB()).process();catch(Exceptione){System.out.print(”Exception“);Whatisthe（ChooseAAExceptionABCompilationfailsbecauseofanerrorinlineCompilationfailsbecauseofanerrorinlineNullPointerExceptionRuntimeException,所以此处不认为子类重写方法抛出了比父类对应方法的异常。QuestionClicktheExhibitbutton.ClassTestExceptionpublicclassTestExceptionextendsException}Class1.publicclassA{publicStringsayo(Stringname)throwsTestException{if(name==null)thrownew7.9.return“o“+10.12.Aprogrammerwantstousethiscodeinan45.Aa=new46.System.out.println(a.sayWhichtwoaretrue?(ChooseTWO)ClassAwillnotLine46canthrowtheuncheckedexceptionLine45canthrowtheuncheckedexceptionLine46willcompileiftheenclosingmethodthrowsaLine46willcompileifenclosedinatryblock,whereTestExceptioniscaught.答案：yzethefollowingtwoclass{staticinta= finalclassSecondextends{void{ 12.（ChooseClassFirstcompiles,butclassSeconddoesNeitherclassBothclassescompile,andifmethod()isinvoked,itwrites3totheBothclassescompile,andifmethod()isinvoked,itthrowsanthis也是可以的，只是不推荐，容易在阅读QuestionWhatwillbetheresultofattemptingtocompileandrunthefollowingObjecto1=newObject();Objecto2=newObject();o1=o2;if(o1.equals(o2)){System.out.pr