异常处理

异常的“多态”特性

（1）可以有多个catch语句块，每个代码块捕获一种异常。在某个try块后面会有两个不同的catch块捕获两个相同类型的异常是语法错误。

（2）使用catch语句，只能捕获Exception类及其子类的对象。因此，一个捕获Exception对象的catch语句块可以捕获所有“可捕获”的异常。

（3）将catch（Exception e）放在别的catch块前面会使这些catch块都不执行，因此Java不会编译这个程序。

package schoolworld;
public class Demo { 
    public static void main(String[] args) { 
        try { 
                try { 
                    throw new ArrayIndexOutOfBoundsException(); 
                } 
                catch(ArrayIndexOutOfBoundsException e) { 
                       System.out.println(  "ArrayIndexOutOfBoundsException" +  "/内层try-catch"); 
                }
 
            throw new ArithmeticException(); 
        } 
        catch(ArithmeticException e) { 
            System.out.println("发生ArithmeticException"); 
        } 
        catch(ArrayIndexOutOfBoundsException e) { 
           System.out.println(  "ArrayIndexOutOfBoundsException" + "/内层try-catch"); 
        } 
    } 
}

上诉代码的运行结果为

ArrayIndexOutOfBoundsException/内层try-catch
发生ArithmeticException

package schoolworld;
public class Demo { 
    public static void main(String[] args) { 
        try {
                try { 
                    throw new ArrayIndexOutOfBoundsException(); 
                } 
                catch(ArithmeticException e) { 
                    System.out.println( "ArrayIndexOutOfBoundsException" + "/内层try-catch"); 
                }
            throw new ArithmeticException(); 
        } 
        catch(ArithmeticException e) { 
            System.out.println("发生ArithmeticException"); 
        } 
        catch(ArrayIndexOutOfBoundsException e) { 
            System.out.println( "ArrayIndexOutOfBoundsException" + "/外层try-catch"); 
        } 
    } 
}

运行结果为

ArrayIndexOutOfBoundsException/外层try-catch

package schoolworld;
public class Demo {
    public static void main(String[] args)
    {        
        try{           
            System.out.println("in main");            
            throw new Exception("Exception is thrown in main");
                    //System.exit(0);
        }        
        catch(Exception e)
            {            
            System.out.println(e.getMessage());            
            System.exit(0);       
        }        
        finally   
        {  
            System.out.println("in finally");
        }
    }
}

运行结果为

in main
Exception is thrown in main