Exception handling mechanism II

Declaration throws an exception
Declaration throw exception is Java The second way to handle exceptions in
1、 If there's a way ( When the statement in is executed ) It may generate some kind of exception , But I'm not sure how to deal with it Species abnormality , This method should explicitly declare that an exception is thrown , Indicates that this method will not handle these exceptions , It's up to the caller of the method to handle .
2、 Use... In the method declaration throws Statement can declare a list of exceptions thrown ,throws The following exception types can be So is the type of exception generated in the method , It can also be its parent class .

Declare an example of throwing an exception ：

Override the principle of method declaration throwing exceptions
An overriding method cannot throw an exception type that is larger than the scope of the overridden method . In the case of polymorphism , Yes methodA() Method call - Exception capture is handled according to the exception declared by the parent class .

Throw an exception manually
Java Exception class objects are automatically generated by the system and Throw out , It can also be manually created and thrown as needed .
1、 First of all, we need to generate exception class objects , And then through throw Statement to implement the throw operation ( Submit to Java shipment Business environment ). IOException e = new IOException();
throw e;
2、 The exception that can be thrown must be Throwable Or an instance of its subclass . The following statement will There will be grammatical errors ：
throw new String(“want to throw”)

User defined exception class
1、 In a general way , User defined exception classes are RuntimeException Subclasses of
2、 Custom exception classes usually need to write several overloaded constructors .
3、 Custom exceptions need to provide serialVersionUID
4、 Custom exception through throw Throw out .
5、 The most important thing about custom exceptions is the name of the exception class , When an exception occurs , According to Name determines the exception type .
User defined exception class MyException, It is used to describe the error information of data value range . user Your own exception class must inherit the existing exception class .

summary ： exception handling 5 Key words