麻烦大家看2个小程序

一:通过方法printStackTrace(),看出重新抛出异常对象,起调用栈信息不变
           package mytool;
           
           class MyException extends Exception
           {
            }
           
           class ReThrowing
           {
                public void f() throws MyException
                {
                     throw new MyException();
                 } 

                public void g() throws MyException
                {
                    try
                    {
                       f();
                     }
                    catch(MyException myE)
                    {
                         System.err.println("catch MyException from f()");
                         myE.printStackTrace();
                         throw myE; 
                     }
                    
                    
                 }

             }

              public class ToTestRethrowing
              {
                public static void main(String[] args) 
                {
                   ReThrowing a = new ReThrowing();
                   try
                   {
                      a.g();
                    }
                   catch(MyException myEe)
                   {
                        System.err.println("catch MyException from g()"); 
                        myEe.printStackTrace();
                    }
                 }
            }


二:通过fillInStackTrace()刷新调用栈信息
           package mytool;
           
           class MyException extends Exception
           {
            }
           
           class ReThrowing
           {
                public void f() throws MyException
                {
                     throw new MyException();
                 } 

                public void g() throws Throwable
                {
                    try
                    {
                       f();
                     }
                    catch(MyException myE)
                    {
                         System.err.println("catch MyException from f()");
                         myE.printStackTrace();
                         throw myE.fillInStackTrace(); 
                     }
                    
                    
                 }

             }

              public class ToTestRethrowing
              {
                public static void main(String[] args) throws Throwable
                {
                   ReThrowing a = new ReThrowing();
                   try
                   {
                      a.g();
                    }
                   catch(MyException myEe)
                   {
                        System.err.println("catch MyException from g()"); 
                        myEe.printStackTrace();
                    }
                 }
            }   

问题: fillInStackTrace()返回的是Trowable对象,应该将方法g()异常声明由MyException改为Trowable即可,mian()方法并不需要抛出异常(如程序一),在程序二中为什么要在main()方法上进行异常声明?