"Java from Beginner to Mastery" Chapter 11th study notes

11th Chapter Exception Handling

I. Classification of anomalies

1, controllable type exception:

(1) IOException: When sending some kind of I/O exception;

(2) SQLException: Exceptions to database access or other errors

(3) ClassNotFoundException: Class not found exception

(4) Nosuchfieldexception: Exception when class does not contain a field with the specified name

(5) Nosuchmethodexception: An exception cannot be found for a method

1  Public classEx1 {2     3     Private intnum=10;4      Public intGetnum () {5         return  This. Num;6     }7      Public voidSetnum (intnum) {8          This. num=num;9     }Ten      PublicEx1 () { One         Try{ AClass.forName ("Ex123");//attempt to load class -}Catch(ClassNotFoundException e) {//Catching exceptions -E.printstacktrace ();//the output method of the exception the         } -SYSTEM.OUT.PRINTLN ("Test! "); -     } -  +      Public Static voidMain (string[] args) { -         //TODO auto-generated Method Stub +Ex1 test=NewEx1 (); ATest.setnum (888); at System.out.println (Test.getnum ()); -     } -}

2. Run-time exception
(1) Indexoutofboundsexception: The index of the collection or array is out of range exception

(2) NullPointerException: The program uses a null exception when the object is needed

(3) ArithmeticException: Anomalies in mathematical operations

(4) IllegalArgumentException: The method passed the illegal parameter

(5) ClassCastException: Forcing an object to be replaced by an exception that is not a subclass of an instance

1  Public classExc2 {2     int[] number={100,80,50,70,20,60};3      Public voidSetnum (intIndexintvalue) {4number[index]=value;5     }6      Public intGetnum (intindex) {7         returnNumber[index];8     }9      Public Static voidMain (string[] args) {TenExc2 test=NewExc2 (); One          for(inti=0;i<=10;i++){ A             Try{ - System.out.println (Test.getnum (i)); -System.out.println ("+i+" array element is displayed normally "); the}Catch(Exception e) { - e.printstacktrace (); -System.out.println ("+i+" element cannot be read!) "); -                  Break; +             } -         } +     } A}

Second, handling exceptions
For statements that may occur in a program, you can add them to a try statement block and handle them appropriately with a catch statement block. There are try-catch statements, and try-catch-finally statements.

Where the finally statement block is the code that executes regardless of whether the program in the TRY statement block has an exception.

Third, practical practice

1 /**2 * Write an exception class myexception, and then write a student class with an speak (int m) method that produces an exception3 * When M is greater than 1000, the method throws the MyException object4 * Through the main class test5  * @authorTS6  */7  Public classtest{8      Public classMyExceptionextendsexception{9          PublicMyException (inti) {TenSystem.out.println ("The value of the exception!i cannot be greater than 1000!") "); OneSystem.out.println ("Current I value is" +i); A         } -     } -      Public classstudent{ the          Public voidSpeakintMthrowsmyexception{ -             if(m>1000){ -                 Throw Newmyexception (m); -}Else{ +SYSTEM.OUT.PRINTLN ("No Exceptions found!") "); -             } +         } A     } at      Public Static voidMain (string[] args) { -Test test=NewTest (); -Student Stu=test.NewStudent (); -         Try{ -Stu.speak (1001); -}Catch(MyException ex) { in ex.printstacktrace (); -         } to     } +}

1 /**2 * Create a number class, with the count () method of the class to get the result of any two numbers added3 * If a negative number is passed to the count () method, a custom exception is thrown4 * Test in the main class5  * @authorTS6  */7  Public classTest {8      Public classnumber{9         LongCountLongMLongNthrowsmyexception{Ten             if((m<0) | | (n<0)){ One                 Throw Newmyexception (); A}Else{ -System.out.println ("return correctly! The result is "+ (m+n)); -                 returnm+N; the             } -         } -     } -      Public classMyExceptionextendsexception{ +          Publicmyexception () { -System.out.println ("throws a custom exception here myexception! "); +System.out.println ("Reminder: There are negative numbers in Addend! "); A         } at     } -      Public Static voidMain (string[] args) { -Test test=NewTest (); -Number Num=test.NewNumber (); -         Try{ -Num.count (12,-15); in}Catch(MyException e) { - e.printstacktrace (); to         } +          -     } the  *}

"Java from Beginner to Mastery" Chapter 11th study notes