Java 1.6中未提供阶乘递归异常

Question

Why I am not getting any Exception in the following code? After running this code I am getting an infinite loop mentioning at test.fact(t.java:32) No Compile-Time Error was found.

class test
{

    int fact(int m) throws Exception
    {
        if (m==1)
        {
        return 1;
        }
    else
        return (fact ((m-1)*m));
    }
}

class main
{
    public static void main(String ar[]) throws Exception
    {
        test t = new test();
        System.out.println(t.fact(5));
    }
}

while say for example i am using

return(a+b); 

it executes successfully whats the problem with the recursion to show an error???

Answer 1

You have a mistake in the return value expression of fact method. It should be

      return fact(m-1) * m;

Answer 2

      return (fact ((m-1)*m));

returns

fact(20)

which returns

fact (380)

which returns

fact (379*380)

which ....

which never returns anything and should make a stack overflow (too much memory is used on the call stack).

           return fact(m-1) * m;

should work.

I highly recommend you reading again the basics, and examples ( here, for example - http://www.toves.org/books/java/ch18-recurex/index.html )

Try writing the recursion tree yoursels, in order to understand what happens.

Answer 3

Another way to calculate factorial using cycle (with no recursion):

int fact(int m) throws Exception
{
    int f = 1;
    for (int i = 0; i < m; f *= ++i);
    return f;
}