java 异常

java中的万物之源是Object,但是java异常中的异常的老祖宗是Throwable。

Throwable下面包括了两大类，它们分别是Error已及Exception，其中Error是指指示合理的应用程序不应该试图捕获的严重问题。那么这句话是什么意思呢？意思就是说当发生这种异常时一般表现为如同系统崩溃之类的大问题，已经没有捕获或者说处理的必要了。而另一个Exception的含义是它指出了合理的应用程序想要捕获的条件。也就是说出现Exception里面的异常，是不会有大问题但是如果不处理的话？在程序运行的时候，会出现问题的。

（补充一句：异常是发生在java运行期间的，不是在javac编译期间的）

另外，Exception里面又包括了两种类型。分别是不常见的异常RuntimeException还有常见的非RuntimeException：

1.RuntimeException又包括了以下几个异常 

ConcurrentModificationException,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 。

     这些异常是指有可能会在代码里面大面积出现，所以没有处理的必要。例如：NullPointerException——空指针异常，只要new了一个对象，并且调用了方法。就有可能会出现这个异常。所以，如果要处理的话，就有可能出现满屏的try······catch.的情况。当满屏异常都处理的情况下，就等于没有处理。

2.非RuntimeException又包括了以下几个异常

 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

这些异常是指只会出现在一些特定的类中如：IOException 这个异常就只会出现在io流当中。