java--simple principle and application of exception handling mechanism

Simple principle and application of exception handling mechanism

Execption can be divided into Java standard definition of exceptions and programmer custom exceptions 2 kinds

(1) One is that when a program violates a Java language rule, the Java Virtual machine represents the error that occurs as an exception. Here the syntax rules refer to the semantic checks built into the Java class library.

For example int i = 2/0 or String str = null;str.length ();

(2) Another case is that Java allows programmers to extend this semantic check, and programmers can create their own exceptions and freely choose when to throw exceptions with the throw keyword.

For example Exception ex = new Exception ("This is my custom exception information"); throw ex;

All exceptions are subclasses of thowable.

Exception handling is parallel to program execution.

try{    // may find exception statement block }catch(exception type, e) {   //  EXECUTE statement block when exception occurs } finnally{  // statement block executed regardless of whether an exception occurred }

Second, the exception of the treatment method

Includes catch exception and top throw exception

1. Catching exceptions

Take the example of capturing int i=2/0

          try  {            int i = 2/0;         Catch (Exception ex) {//  The parent class of all exceptions exception            ex.printstacktrace ()            ; // Handling Exceptions            SYSTEM.OUT.PRINTLN ("Exception information:" + ex.getmessage ());        }          finally {            System.out.println ("Free resources, subsequent code, code that must be executed");        }        System.out.println ("continue running");

The output result is

Ex.printstacktrace () indicates that detailed exception information is printed to the console

2, top throw abnormal throws

With String str =null;

Str.length (); (not instantiated) as an example

 Packagetest;ImportCom.hanqi.ThrowEX; Public classTest { Public voidTest ()throwsException {//with throws String Str=NULL;    Str.length (); }     Public Static voidMain (string[] args) {Throwex te=NewThrowex (); With throwTry{te.test (); } Catch(Exception e) {//TODO Auto-generated catch blockE.printstacktrace (); System.out.println ("Exception information is" +e.getmessage ()); }    }}

E.printstacktrace () indicates that detailed exception information is printed to the console

java--simple principle and application of exception handling mechanism