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  • 动手动脑(课堂作业06)

    1,请阅读并运行AboutException.java示例,然后通过后面的几页PPT了解Java中实现异常处理的基础知识。

     1 import javax.swing.*;
     2 
     3 class AboutException {
     4    public static void main(String[] a) 
     5    {
     6       int i=1, j=0, k;
     7       k=i/j;
     8 
     9 
    10     try
    11     {
    12         
    13         k = i/j;    // Causes division-by-zero exception
    14         //throw new Exception("Hello.Exception!");
    15     }
    16     
    17     catch ( ArithmeticException e)
    18     {
    19         System.out.println("被0除.  "+ e.getMessage());
    20     }
    21     
    22     catch (Exception e)
    23     {
    24         if (e instanceof ArithmeticException)
    25             System.out.println("被0除");
    26         else
    27         {  
    28             System.out.println(e.getMessage());
    29             
    30         }
    31     }
    32 
    33     
    34     finally
    35      {
    36              JOptionPane.showConfirmDialog(null,"OK");
    37      }
    38         
    39   }
    40 }

    运行结果为:

    不难看出,这是程序出错,但这并没有抛出异常,程序运行到第一个k=i/j就出错了,将其注释掉后运行结果为:

    Java中的异常捕获语句:

    Try

    {

    //可能发生运行错误的代码;

    }

    catch(异常类型 异常对象引用)

    {

    //用于处理异常的代码

    }

    finally

    {

    //用于“善后” 的代码

    }

     Java 中所有可捕获的异常都派生自 Exception 类。

    2,

    使用javap去反汇编两个示例程序的.class文件

    第一个反编译得:

     

    第二个反编译得:

     

    3,阅读以下代码(CatchWho.java),写出程序运行结果:

     1 public class CatchWho { 
     2     public static void main(String[] args) { 
     3         try { 
     4                 try { 
     5                     throw new ArrayIndexOutOfBoundsException(); 
     6                 } 
     7                 catch(ArrayIndexOutOfBoundsException e) { 
     8                        System.out.println(  "ArrayIndexOutOfBoundsException" +  "/内层try-catch"); 
     9                 }
    10  
    11             throw new ArithmeticException(); 
    12         } 
    13         catch(ArithmeticException e) { 
    14             System.out.println("发生ArithmeticException"); 
    15         } 
    16         catch(ArrayIndexOutOfBoundsException e) { 
    17            System.out.println(  "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
    18         } 
    19     } 
    20 }

    预测结果:

    ArrayIndexOutOfBoundsException/内层try-catch
    发生ArithmeticException

    我认为try里面的代码throw new ArrayIndexOutOfBoundsException先抛出ArrayIndexOutOfBoundsException类型的异常,于是System.out.println(  "ArrayIndexOutOfBoundsException" +  "/内层try-catch");之后throw new ArithmeticException();于是System.out.println("发生ArithmeticException");

    运行结果:

    4,写出CatchWho2.java程序运行的结果

     1 public class CatchWho2 { 
     2     public static void main(String[] args) { 
     3         try {
     4                 try { 
     5                     throw new ArrayIndexOutOfBoundsException(); 
     6                 } 
     7                 catch(ArithmeticException e) { 
     8                     System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch"); 
     9                 }
    10             throw new ArithmeticException(); 
    11         } 
    12         catch(ArithmeticException e) { 
    13             System.out.println("发生ArithmeticException"); 
    14         } 
    15         catch(ArrayIndexOutOfBoundsException e) { 
    16             System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
    17         } 
    18     } 
    19 }

    预测结果:

    ArrayIndexOutOfBoundsException/外层try-catch

    我认为throw new ArrayIndexOutOfBoundsException();之后就到了System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 不再往回运行

    运行结果:

    5,

     1 public class EmbededFinally {
     2 
     3     
     4     public static void main(String args[]) {
     5         
     6         int result;
     7         
     8         try {
     9             
    10             System.out.println("in Level 1");
    11 
    12            
    13              try {
    14                 
    15                 System.out.println("in Level 2");
    16   // result=100/0;  //Level 2
    17                
    18                  try {
    19                    
    20                      System.out.println("in Level 3");
    21                       
    22                      result=100/0;  //Level 3
    23                 
    24                 } 
    25                 
    26                 catch (Exception e) {
    27                     
    28                     System.out.println("Level 3:" + e.getClass().toString());
    29                 
    30                 }
    31                 
    32                 
    33                 finally {
    34                     
    35                     System.out.println("In Level 3 finally");
    36                 
    37                 }
    38                 
    39                
    40                 // result=100/0;  //Level 2
    41 
    42             
    43                 }
    44             
    45             catch (Exception e) {
    46                
    47                  System.out.println("Level 2:" + e.getClass().toString());
    48            
    49              }
    50              finally {
    51                 
    52                 System.out.println("In Level 2 finally");
    53            
    54              }
    55              
    56             // result = 100 / 0;  //level 1
    57         
    58         } 
    59         
    60         catch (Exception e) {
    61             
    62             System.out.println("Level 1:" + e.getClass().toString());
    63         
    64         }
    65         
    66         finally {
    67            
    68              System.out.println("In Level 1 finally");
    69         
    70         }
    71     
    72     }
    73 
    74 }

    预测结果:

    in Level 1
    in Level 2
    in Level 3
    Level 3:class java.lang.ArithmeticException
    In Level 3 finally
    In Level 2 finally
    In Level 1 finally

    程序一个一个try往下运行,于是输出in Level 1
    in Level 2
    in Level 3

     因为result=100/0;所以出了异常输出Level 3:class java.lang.ArithmeticException

    紧接着另外两个try都没出异常正常运行finally依次输出

    In Level 3 finally
    In Level 2 finally
    In Level 1 finally

    运行结果:

    6,

     1 public class SystemExitAndFinally {
     2 
     3     
     4     public static void main(String[] args)
     5     {
     6         
     7         try{
     8 
     9             
    10             System.out.println("in main");
    11             
    12             throw new Exception("Exception is thrown in main");
    13 
    14                     //System.exit(0);
    15 
    16         
    17         }
    18         
    19         catch(Exception e)
    20 
    21             {
    22             
    23             System.out.println(e.getMessage());
    24             
    25             System.exit(0);
    26         
    27         }
    28         
    29         finally
    30         
    31         {
    32             
    33             System.out.println("in finally");
    34         
    35         }
    36     
    37     }
    38 
    39 
    40 }

     运行结果:

    原因:因为程序里有System.exit(0);,运行完catch就结束程序运行了。

    7,如何跟踪异常的传播路径?

    当程序中出现异常时,JVM会依据方法调用顺序依次查找有关的错误处理程序。 可使用printStackTrace 和 getMessage方法了解异常发生的情况: printStackTrace:打印方法调用堆栈。 每个Throwable类的对象都有一个getMessage方法,它返回一个字串,这个字串是在Exception构造函数中传入的,通常让这一字串包含特定异常的相关信息。

    // UsingExceptions.java
    // Demonstrating the getMessage and printStackTrace
    // methods inherited into all exception classes.
    public class PrintExceptionStack {
       public static void main( String args[] )
       {
          try {
             method1();
          }
          catch ( Exception e ) {
             System.err.println( e.getMessage() + "
    " );
             e.printStackTrace();
          }
       }
    
       public static void method1() throws Exception
       {
          method2();
       }
    
       public static void method2() throws Exception
       {
          method3();
       }
    
       public static void method3() throws Exception
       {
          throw new Exception( "Exception thrown in method3" );
       }
    }

    运行结果:

    8,

    因为他没有添加异常抛出:

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  • 原文地址:https://www.cnblogs.com/chch157/p/7847159.html
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