java异常

• 分类：throwable的子类
  有 Error 和 Exception

1. Error:一般是指与虚拟机相关的问题，如系统崩溃，虚拟机错误，内存空间不足，方法调用栈溢等。对于这类错 误的导致的应用程序中断，仅靠程序本身无法恢复和和预防，遇到这样的错误，建议让程序终止。

/**
 * An {@code Error} is a subclass of {@code Throwable}
 * that indicates serious problems that a reasonable application
 * should not try to catch. Most such errors are abnormal conditions.
 * The {@code ThreadDeath} error, though a "normal" condition,
 * is also a subclass of {@code Error} because most applications
 * should not try to catch it.
 * 

 * A method is not required to declare in its {@code throws}
 * clause any subclasses of {@code Error} that might be thrown
 * during the execution of the method but not caught, since these
 * errors are abnormal conditions that should never occur.
 *
 * That is, {@code Error} and its subclasses are regarded as unchecked
 * exceptions for the purposes of compile-time checking of exceptions.

2. Exception:表示程序可以处理的异常，可以捕获且可能恢复。遇到这类异常，应该尽可能处理异常，使程序恢复运行，而不应该随意终止异常。

**
 * The class {@code Exception} and its subclasses are a form of
 * {@code Throwable} that indicates conditions that a reasonable
 * application might want to catch.
 *
 * 
The class {@code Exception} and any subclasses that are not also
 * subclasses of {@link RuntimeException} are checked
 * exceptions.  Checked exceptions need to be declared in a
 * method or constructor's {@code throws} clause if they can be thrown
 * by the execution of the method or constructor and propagate outside
 * the method or constructor boundary.

---

• 其中Exception可分为2种：

1. RuntimeException：运行期异常，系统异常
   可以处理也可以不处理，编译器不强制用 try..catch 处理或用 throws 声明，所以系统异常也称为 unchecked 异常。
   eg：NullPointerException,IndexOutOfBoundsException,ClassCastException,ClassNotFoundException ， IllegalArgumentException，UnsupportedOperationException。

2. CheckedException: 也成编译器异常
   编译器强制普通异常必须 try..catch 处理或用 throws 声明继 续抛给上层调用方法处理
   eg：CloneNotSupportedException