Difference and understanding between detected and non detected anomalies

1、 B. abnormal

The so-called checked exception actually indicates that it is at the time of compilation , Exceptions to force check , This exception needs to be displayed through try/catch To capture or through throws Throw it out, otherwise the program cannot be compiled .

2、 Undetected abnormal

The so-called unchecked exception means that the compiler does not need to force to check the exception , This exception does not need to be displayed to catch or throw .

stay java All exceptions inside need to be inherited java.lang.Throwable This class is shown below ：

Throwable There are two direct subclasses ：

1. Error： It refers to errors at the bottom of the program or at the hardware level , Like the usual OOM abnormal （ Memory overflow exception ） So this exception has nothing to do with the program itself, so it doesn't need to check whether it belongs to Undetected abnormal .
2. Exception： It indicates some exceptions in the program , It may be caused by lax procedures, such as NullPointerException（ Null pointer exception ） etc. ,Exception Two exception types are derived
   1. RuntimeException： The runtime exception belongs to the non inspected exception
   2. other Exception

Summary ：

So in addition to Error and RuntimeException as well as RuntimeException Outside the derived class of , Other exceptions belong to the detected exceptions, such as ：IOException and SQLException, In fact, the reason is Java I think the main reason for designing some exceptions for mandatory inspection is ：

Consider the correctness of the program 、 stability 、 reliability , As mentioned above, database exceptions are unexpected exceptions of the program, but once there is a problem, it will cause an occupation of resources and cause some problems in the program , So we need to catch these problems. Once there is a problem, we can deal with it in time , If we operate the database try/catch And then finally close xxx.close Close the connection , So generally speaking, the detected exception is an exception that cannot be judged in the program. Let's use try/catch Capture .