Java can't find main(String[]) method in class

Lautturi.java

import java.util.*;

public class Lautturi {

	public static void main(String[] args) {
		int num;    
		Object obj_01 = new Object();    
		num=obj_01.hashCode();
		System.out.println("Hash Code of the object is: " + num);
	}

}

• the file name Lautturi must be same as class name.
• the main function must be "public static void".
• are there other classes?