Java课件_LESSON 7 - Exceptions.pptVIP

LESSON 6: Exceptions 吴砥 wudi@ Department of Electronics Information Engineering, Huazhong University of Science Technology, Wuhan, P.R.C. The eight core packages of Java java.awt java.awt.event java.io java.sql java.util java.lang java.applet Outline Problem What is Exception The types of Exceptions Exception processing Summary Problem To read a file 1 No exception handling Open the file Get the file size Allocate memory space Read data from the file Close the file To read a file 2 Traditional exception handling IF open the file successfully THEN IF allocate memory space successfully THEN IF read data successfully THEN IF close file successfully THEN EXIT ELSE … ELSE … ELSE … ELSE … To read a file 3 Exception handling in Java try { Open the file Get the file size Allocate memory space Read data from the file Close the file } catch(open file exception) {…} catch(allocate memory space exception) {…} … What is Exception An Exception An exception is an indication that a problem occurred during the program’s execution. An exception is any object that is an instance of the class Throwable (or any of its subclasses). The features of exceptions The extensibility of Java can increase the number and types of errors that can occur. Every new class can add its own error possibilities. Exception handling enable programmers to write clearer, more robust, more fault-tolerant programs Why need exceptions Exception handling should be used to process exceptional situations where a method is unable to complete its task for reasons it cannot control, to process exceptions from program components that are not geared to handling those exceptions directly, or on large projects to handle exceptions in a uniform manner project wide Main exceptions ArithmeticException ArrayIndexOutOfBandsException ArrayStoreException IOException FileNotFoundException NullPointerException MalformedURLException NumberFormatException OutOfMemoryException Sample code The class Throwable The Throwable cla