AOOTWeek2 Unchecked和Checked Exception的理解

什么是unchecked异常?

即RuntimeException（运行时异常）

不需要try...catch...或throws 机制去处理的异常



列举最常用的五种RuntimeException:     

这是JAVA认证考试中最常见的题目,事实上,runtime exception中最常见的,经常碰到的,也就5,6种,如下:
 
ArithmeticException
 
ClassCastException：
 
IndexOutOfBoundsException
    
ArrayIndexOutOfBoundsException,
    
StringIndexOutOfBoundsException

IllegalArgumentException
   
NumberFormatException

NullPointerExceptionextends
   



除了RuntimeException，其他继承自java.lang.Exception得异常统称为Checked Exception,他们有多少种呢?

下面是JDK API中列出的异常类:

除了RuntimeException以外的,都是checked Exception

java.lang.Object
  java.lang.Throwable
      java.lang.Exception

所有已实现的接口：
Serializable

直接已知子类：
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, RuntimeException, SAXException, ScriptException, ServerNotActiveException, SOAPException, SQLException, TimeoutException, TooManyListenersException, TransformerException, TransformException, UnmodifiableClassException, UnsupportedAudioFileException, UnsupportedCallbackException, UnsupportedFlavorException, UnsupportedLookAndFeelException, URIReferenceException, URISyntaxException, UserException, XAException, XMLParseException, XMLSignatureException, XMLStreamException, XPathException

我们这里没有必要讨论checked异常的合理性，但我们需要知道的是，它对程序员是一个提醒的

作用，即提醒编程者注意这里可能有异常抛出，需要处理或交给上层调用者。