Java Study Notes 12 -- Exception Handling and Study Notes 12 --

Java Study Notes 12 -- Exception Handling and Study Notes 12 --

Java learning notes series:

Java study note 11-Summary

Java Study Notes 10-generic Summary

Java study notes 9-internal class Summary

Java study note 8-interface Summary

Java study notes 7 -- abstract classes and abstract methods

Java study Note 6-class inheritance, Object class

Java study notes 5-Class Method

Java study note 4-object initialization and collection

Java Study Notes 3-Basics of classes and objects

Java study Note 2 -- data type, array

Java study Note 1-Summary of the development environment Platform

URL: http://www.cnblogs.com/archimedes/p/java-study-note12.html.

1. Exception Handling Overview

An example of reading two integers and displaying the operator:

public static void main(String args[]){    Scanner input = new Scanner(System.in);      System.out.print("Enter two integers: ");    int number1 = input.nextInt();    int number2 = input.nextInt();     System.out.println(number1 + " / " + number2 + " is " + (number1 / number2)); }

Enter two integers: 3 0

Exception in thread "main" java. lang. ArithmeticException:/by zero
At Main. main (Main. java: 18)

A simple solution is to add an if statement to test the second number:

public class Main{    public static void main(String args[])    {        Scanner input = new Scanner(System.in);                System.out.print("Enter two integers: ");        int number1 = input.nextInt();        int number2 = input.nextInt();        if(number2 != 0)            System.out.println(number1 + " / " + number2 + " is " + (number1 / number2));        else            System.out.println("Divisor cannot be zero ");    }}

To demonstrate the concept of exception handling, including how to create, throw, capture, and handle exceptions, rewrite the above program as follows:

public class Main{    public static void main(String args[])    {        Scanner input = new Scanner(System.in);                System.out.print("Enter two integers: ");        int number1 = input.nextInt();        int number2 = input.nextInt();        try {            if(number2 == 0)                throw new ArithmeticException("Divisor cannot be zero");            System.out.println(number1 + " / " + number2 + " is " + (number1 / number2));        }        catch(ArithmeticException ex) {            System.out.println("Exception: an integer " + "cannot be divided by zero ");        }        System.out.println("Execution continues ...");    }}

2. Benefits of Exception Handling

Use the following method to calculate the problem:

public class Main{    public static int quotient(int number1, int number2) {        if(number2 == 0)            throw new ArithmeticException("Divisor cannot be zero");        return number1 / number2;    }        public static void main(String args[])    {        Scanner input = new Scanner(System.in);                System.out.print("Enter two integers: ");        int number1 = input.nextInt();        int number2 = input.nextInt();        try {            int result = quotient(number1, number2);            System.out.println(number1 + " / " + number2 + " is " + result);        }        catch(ArithmeticException ex) {            System.out.println("Exception: an integer " + "cannot be divided by zero ");        }        System.out.println("Execution continues ...");    }}

The advantage of exception handling is to separate detection errors from handling errors.

3. Exception type

4. More about Exception Handling

Java Exception Handling model is based on three operations:Declare an exception, throw an exception, and capture an exception

Declared exception

If an exception is declared in a method, the keyword throws is used in the method header, as shown below:

public void myMethod throws Exception1,Exception2,……,ExceptionN

Throw an exception

A program that detects an error can create an instance of the correct exception type and throw it

Instance:

IllegalArgumentException ex = new IllegalArgumentException("Worng Argument");throw ex;

Or directly:

throw new IllegalArgumentException("Worng Argument");

Capture exceptions

When an exception is thrown, you can capture and process it in try-catch:

try {    statements;} catch (exception1 ex1){    handler for exception1;} catch (exception1 ex2){    handler for exception2;} ……catch (exception1 exN){    handler for exceptionN;}    

Obtain information from exceptions

You can use the methods in the Throwable class to obtain the exception information.

public class test {    public static void main(String[] args) {        try {            System.out.println(sum(new int[]{1,2,3,4,5}));        } catch(Exception ex) {            ex.printStackTrace();            System.out.println(ex.getMessage());            System.out.println(ex.toString());            System.out.println("Trace Info Obtained from getBackTrace");            StackTraceElement[] traceElements = ex.getStackTrace();            for(int i = 0; i < traceElements.length; i++) {                System.out.print("monthod " + traceElements[i].getMethodName());                System.out.println("(" + traceElements[i].getClassName());                System.out.println(traceElements[i].getLineNumber() + ")");            }        }    }        private static int sum(int[] list) {        int sum = 0;        for(int i = 0; i <= list.length; i++) {            sum += list[i];        }        return sum;    }}

Finally statement

Whether or not an exception occurs, you want to execute some code. You can use the finally clause:

public class test {    public static void main(String[] args) {        PrintWriter output = null;        try {            output = new PrintWriter("wu.txt");            output.println("wlecome tio java");        } catch(IOException ex) {            ex.printStackTrace();        } finally {            if(output != null)                output.close();        }        System.out.println("End of the program");    }}