Java exception handling and use of custom exceptions

1. Introduction to Exceptions

The abnormal mechanism can improve the robustness and fault tolerance of the program.

Throwable:throwable is a superclass of all errors or exceptions in the Java language. There are two sub-classes of error and exception.

1.1 Compile-time exception

　　The compile-time exception must be handled or the compilation cannot pass.

Aclnotfoundexception, Activationexception, Alreadyboundexception, ApplicationException, AWTException, Backingstoreexception, Badattributevalueexpexception, Badbinaryopvalueexpexception, BadLocationException, Badstringoperationexception, Brokenbarrierexception, Certificateexception, ClassNotFoundException, Clonenotsupportedexception, Dataformatexception, Datatypeconfigurationexception, DestroyFailedException, Executionexception, Expandvetoexception, Fontformatexception, Generalsecurityexception, GSSException, Illegalaccessexception, Illegalclassformatexception, Instantiationexception, Interruptedexception, Introspectionexception, Invalidapplicationexception, Invalidmididataexception, Invalidpreferencesformatexception, Invalidtargetobjecttypeexception, InvocationTargetException, IOException, Jaxbexception, JMException, Keyselectorexception, Lastownerexception, Lineunavailableexception, Marshalexception, MidiUnavailableException, Mimetypeparseexception, Mimetypeparseexception, NAMINGEXCEPtion, noninvertibletransformexception, nosuchfieldexception, Nosuchmethodexception, NotBoundException, Notownerexception, ParseException, Parserconfigurationexception, PrinterException, PrintException, Privilegedactionexception, Propertyvetoexception, Refreshfailedexception, Remarshalexception, SAXException, Scriptexception, Servernotactiveexception, SoapException, SQLException, TimeoutException, toomanylistenersexception , Transformerexception, Transformexception, Unmodifiableclassexception, Unsupportedaudiofileexception, Unsupportedcallbackexception, Unsupportedflavorexception, Unsupportedlookandfeelexception, URIReferenceException, URISyntaxException, Userexception, Xaexception, Xmlparseexception, Xmlsignatureexception, XMLStreamException, XPathException

　

1.2 Run-time exception ( RuntimeException)

Annotationtypemismatchexception, ArithmeticException, Arraystoreexception, Bufferoverflowexception, Bufferunderflowexception, Cannotredoexception, Cannotundoexception, ClassCastException, CMMException, Concurrentmodificationexception, Domexception, Emptystackexception, Enumconstantnotpresentexception, Eventexception, IllegalArgumentException, Illegalmonitorstateexception, Illegalpathstateexception, IllegalStateException, Imagingopexception, Incompleteannotationexception, Indexoutofboundsexception, Jmruntimeexception, Lsexception, Malformedparameterizedtypeexception, Mirroredtypeexception, Mirroredtypesexception, MissingResourceException, Negativearraysizeexception, Nosuchelementexception, Nosuchmechanismexception, NullPointerException, Profiledataexception, ProviderException, RasterFormatException, Rejectedexecutionexception, SecurityException, SystemException, Typeconstraintexception, TypeNotPresentException, Undeclaredthrowableexception, Unknownannotationvalueexception, UnknownelemenTexception, Unknowntypeexception, Unmodifiablesetexception, Unsupportedoperationexception, WebServiceException 

NullPointerException and Indexoutofboundsexception are common run-time anomalies.

Example:

    Public Static void Main (string[] args) {        intnewint[ten];         NULL ;        System.out.println (Array.Length);    }

Exception in thread "main" Java.lang.NullPointerExceptionat Lang. Object.ExceptionTest.main (EXCEPTIONTEST.JAVA:18)

About the NPE exception

This exception is thrown when an application tries to use the object where it is needed null . This situation includes:

• Invokes null an instance method of an object.
• Access or modify null The fields of an object.
• will be null used as an array to get its length.
• will be null used as an array to access or modify its time slice.
• Will null be Throwable thrown as a value.

An application should throw an instance of the class, indicating other null illegal use of the object.

2. Handling of abnormal operation period

Exceptions can be captured using catch and then processed.

    @Test    publicvoid  testarithmeticexception () {        try  {             int result = 10/0;            System.out.println ("code after exception in try will not execute");         Catch (ArithmeticException e) {            System.out.println ("Exception handling:");            System.out.println (E.getmessage ());        }        System.out.println ("code after Try...catch can be executed");    }

3. Throw of the run-time exception

　　Without processing, the exception can be thrown to the upper layer for processing by the upper layer.

     Public Static voidMain (string[] args) {Try{testnullpointerexception (); } Catch(NullPointerException e) {e.printstacktrace (); System.out.println ("Exceptions are handled by the upper layer"); }        //If an exception occurs in the preceding code, the following code will not executeSystem.out.println ("Call succeeded"); }     Public Static voidtestnullpointerexception () {int[] Array =New int[10]; Array=NULL; //because the performer does not handle the exception, the exception is automatically thrown        intLength =Array.Length;    System.out.println (length); }

Java exception handling and use of custom exceptions