SCJA Java Examples

[Hrishikesh Pramod]

Hi,
I am currently studying for the SCJA Exam. I was writing a program called Factorial3.java from the book Java Examples in a nutshell.
I wrote the program, and after i compiled it and ran it, it said

Exception in thread "main" java.lang.NoSuchMethodError: main

Here is the Program:

public class Factorial3 {
  static long[] table = new long [21];
  static{ table[0] = 1; }
  static int last = 0;

  public static long factorial(int x) throws IllegalArgumentException {
  if (x >= table.length)
    throw new IllegalArgumentException("Overflow; x is too large.");
  if (x < 0) throw new IllegalArgumentException("x must be non-negative.");

  while(last < x) {
      table[last + 1] = table[last] * (last + 1);
      last++;
    }
    return table[x];
  }
}   

Please Help!!
Thanks

[Hrishikesh Pramod]

BTW, I am 13 and I want to take the SCJA.Is it allowed?
Thanks..

[Jeanne Boyarsky]

Welcome to CodeRanch!

I added code tags to make the code more readable. Yes, you are allowed to take the test at 13. As long as your parents are ok with using their credit card to pay for it.

Java is telling you that you don't have a main method. To run a class at the command line, it needs a method that looks like this:

public static void main(String[] args) {

}

You would then call factorial(42) from the main method and it would run the rest of the code.

[Hrishikesh Pramod]

Thank you Jeanne

[Mala Gupta]

Hrishikesh,

As mentioned by Jeanne, you need to add a 'main' method to your class Factorial3, so that you can execute it as a Java application, as follows:

public class Factorial3 {
	static long[] table = new long [21];
	static{ table[0] = 1; }
	static int last = 0;

	public static long factorial(int x) throws IllegalArgumentException {
		if (x >= table.length)
			throw new IllegalArgumentException("Overflow; x is too large.");
		if (x < 0) throw new IllegalArgumentException("x must be non-negative.");

		while(last < x) {
			table[last + 1] = table[last] * (last + 1);
			last++;
		}
		return table[x];
	}

	public static void main (String[] args) {
		// Evaluate and return factorial of 5
		System.out.println (factorial (5));

		// Evaluate and return factorial of 15
		System.out.println (factorial (15));
	}
}

Note that both 'main' and 'factorial' are static methods - methods that do not need existence of a class object to execute.

cheers
Mala

[Hrishikesh Pramod]

Thanks!