Java Exception

水深无声 2022-08-10 03:40 166阅读 0赞

# 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 ##

![call satck][]

# 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 ##

![throwable class][]

### 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/][https_docs.oracle.com_javase_tutorial_essential_exceptions] #

[call satck]: /images/20220731/c5f527d4d26640a4a72906a4a928be4a.png
[throwable class]: /images/20220731/e5337ea37577426fa15a8dac0c82858f.png
[Chained Exceptions]: https://docs.oracle.com/javase/tutorial/essential/exceptions/chained.html
[https_docs.oracle.com_javase_tutorial_essential_exceptions]: https://docs.oracle.com/javase/tutorial/essential/exceptions/