Java Exception

An exception is an event,which occurs during the execution of a program,that disrupts the normal flow of the program’s instructions–Oracle Java doc

当方法中发生错误，方法创建一个对象并把它传递给运行时系统。对象被称为异常对象；创建一个异常对象并传递给运行时系统叫做抛出异常。

Call Stack

Three Kind of Exception

checked exception

all exceptions are checked exceptions,except for :Error,RuntimeException and their subclasses

error

application can not anticipate(预见)or recover from;Errors are not subject to the catch or specify requirement.

runtime exception

indicate programming bugs.

catching and handling Exceptions

try block

try{    //code}

catch block

try{}catch(ExceptionType1 e1){}catch(ExceptionType2 e2){}

catch more than one one type of exception with one Exception Handler

use ‘|’

catch(IOException|SQLException ex){    logger.log(ex);    throw ex;}

try-with-resources statement

package tij.javaexception;import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.FileReader;import java.io.IOException;import java.nio.charset.Charset;import java.nio.charset.StandardCharsets;import java.nio.file.Files;import java.nio.file.Path;import java.nio.file.Paths;import java.util.zip.ZipFile;/** * Created by Administrator on 2015/11/7. */public class TryWithResourse {    //如果readline和close方法同时抛出异常    //readFirstLineFromFileWithFinallyBlock方法将抛出finally块中的异常    //try块中抛出的异常将被抑制    static String readFirstLineFromFileWithFinallyBlock(String path)            throws IOException {        BufferedReader br = new BufferedReader(new FileReader(path));        try {            return br.readLine();        } finally {            if (br != null) br.close();        }    }    //如果try块和try-with-resources都抛出异常    //那么readFirstLineFromFile方法将抛出try块中的异常    //try-with-resources中的异常将被抑止    static String readFirstLineFromFile(String path) throws IOException {        //try-with-resources statement        //br会被close不管try语句是正常的完成了还是突然的完成了.        try(BufferedReader br=        new BufferedReader(new FileReader(path))        ){            return br.readLine();        }    }    /*    try-with-resources语句可以抛出异常    在下面这个方法中try块中抛出一个异常，try-with-resources中抛出俩异常    当try块中抛出一个异常，try-with-resources中抛出一到多个异常的时候    try-with-resources中抛出的异常被抑止    try块中的异常被方法writeToFileZipFileContent抛出    被抑止的异常可以通过调用try块抛出的异常的Throwable.getSuppressed方法提取出来     */    public static void writeToFileZipFileContent(String zipFileName,String outputFileName) throws IOException{        Charset charset= StandardCharsets.UTF_8;        Path path= Paths.get(outputFileName);        //打开zip文件，并创建输出文件用try-with-resource语句        //当直接跟随的代码块终止时，不管是因为正常执行还是出现异常        //zipFile,writer对象的close方法都被按顺序自动调用        //close方法的调用顺序与创建对象的顺序相反.        try(                ZipFile zipFile=new ZipFile(zipFileName);                BufferedWriter writer= Files.newBufferedWriter(path,charset);        ){        }    }    //try-with-resources 语句可以跟catch和finally，但是它们是在声明的资源被关闭后执行的.}

How to throw Exceptions

all methods use throw statement to throw an Exception

throw someThrowableObject;／／Throwable 类的子类

Throwable class and It’s Subclasses

Error class

当动态链接失败或者虚拟机硬件错误出现，虚拟机抛出Error

Exception class

一个Exception类表明一个问题出现了，但不是严重的系统问题
RuntimeException表明对API的错误使用

Chained Exceptions

Chained Exceptions

总结

程序可以用异常来表明一个错误的出现。用throw来抛出异常并提供一个异常对象－Throwable类的子类对象。一个抛出未捕获的受检查异常的方法必须在方法声明中包括一个throws子句。

• try语句块用来识别一块会出现异常的代码
• catch块用来异常处理，处理特定的异常
• finally语句块保证执行，用来关闭文件，恢复资源除此之外在try中代码之后进行清理。

try语句至少包含一个catch块或者一个finally块和多个catch块

参考来源：https://docs.oracle.com/javase/tutorial/essential/exceptions/