How do I throw an exception when I receive a signal?

Is my solution for the following Java exception problem is correct?

• The following problem is taken from SCJP Kathy Sierra book Propagating and Catching an Exception In this exercise you're going to create two methods that deal with exceptions. One of the methods is the main() method, which will call another method. If an exception is thrown in the other method, main() must deal with it. A finally statement will be included to indicate that the program has completed. The method that main() will call will be named reverse, and it will reverse the order of the characters in a String. If the String contains no characters, reverse will propagate an exception up to the main() method. Create a class called Propagate and a main() method, which will remain empty for now. Create a method called reverse. It takes an argument of a String and returns a String. In reverse, check if the String has a length of 0 by using theString.length() method. If the length is 0, the reverse method will throw an exception. Now include the code to reverse the order of the String. Because this isn't the main topic of this chapter, the reversal code has been provided, but feel free to try it on your own. String reverseStr = "";                    for(int i=s.length()-1;i>=0;--i) {                      reverseStr += s.charAt(i);                    }           return reverseStr; Now in the main() method you will attempt to call this method and deal with any potential exceptions. Additionally, you will include a finallystatement that displays when main() has finished. My solution: public class Propagate {   public static void main(String[] args){     try{        System.out.println(reverse("") + "String reversed");     }catch (Exception ex){     System.out.println("the String length is 0");     }finally{      System.out.println("We have successfully completed and coded the problem");    } } public static String reverse(String input){   //Even if I include throws //exception here, it doesn't make any difference    StringBuilder output = new StringBuilder();    for(int i = input.length() - 1; i >=0; --i){        output.append(input.charAt(i));     }    return output.toString(); } }

• Answer:

  You're close but you have not done this part yet: In reverse, check if the String has a length of 0 by using the String.length() method. If the length is 0, the reverse method will throw an exception. Read back about the "throws" and "throw" keywords and look here http://docs.oracle.com/javase/tutorial/essential/exceptions/throwing.html