throw Exception 抛异异常

   if(this.aop == null)throw new NullPointerException("aop is null");  
   if(method == null)throw new NullPointerException("method is null");  

if(something==null)
　　　　　  throw new NullPointerException();　
　　　　else 
　　 　　 　 return "something";


 public Object sell(){  
         if(checkUser())
             Object obj = new Object();  

             return obj ;  
         }else{  
             throw new RuntimeException();  
         }  
     }  

if (t == null) {throw new NullPointerException("something bad");}
if (o == null) throw new NullPointerException(); 


算术异常类：ArithmeticExecption
空指针异常类：NullPointerException
类型强制转换异常：ClassCastException
数组负下标异常：NegativeArrayException
数组下标越界异常：ArrayIndexOutOfBoundsException
违背安全原则异常：SecturityException
文件已结束异常：EOFException
文件未找到异常：FileNotFoundException
字符串转换为数字异常：NumberFormatException
操作数据库异常：SQLException
输入输出异常：IOException
方法未找到异常：NoSuchMethodException