jiecheng.java

自己做的小程序

package mypackage;

import java.math.BigInteger;
import java.util.*;

public class JieCheng {
  protected static ArrayList table = new ArrayList();
  static {
    table.add(BigInteger.valueOf(1));
  }

  public static synchronized BigInteger factorial(int x){
   if(x<0) throw new IllegalArgumentException("x must be non-negative");
   for(int size = table.size();size<=x;size++){
       BigInteger lastfact = (BigInteger)table.get(size-1);
       BigInteger nextfact = lastfact.multiply(BigInteger.valueOf(size));
       table.add(nextfact);
       }
       return (BigInteger) table.get(x);
   }

   public static void main(String args[]){
       int i=60;
       System.out.println(factorial(i));
   }
  }