//例4.9
public class tt
{
  static double sqrt(double i) throws IllegalArgumentException
  {
    if(i<0)
    {
       IllegalArgumentException e=new IllegalArgumentException("不能求負(fù)數(shù)的平方根");
       throw e;
    }
    return(Math.sqrt(i));
  }
  public static void main(String args[])
  {
  	System.out.println("IllegalArgumentException example");
  	try
  	{
  	  System.out.println(sqrt(4));	
  	}
  	catch(IllegalArgumentException e)
  	{ System.out.println("\t捕獲異常："+e); }
  }
}