Java Exception

[cakka]

Hello,

I got this question from my quiz :

Consider the following code (assume that comments are replaced with real code that works as specified):

public class TestExceptions {

    static void e() {
      // Might cause any of the following unchecked exceptions to be
      // thrown:
      // Ex1, Ex2, Ex3, Ex4
    }

    static void April() {
      try {
          e();
      } catch (Ex1 ex) {
          System.out.println("April caught Ex1");
      }
    }

    static void March() {
      try {
          April();
      } catch (Ex2 ex) {
          System.out.println("March caught Ex2");
          // now cause exception Ex1 to be thrown
      }
    }

    static void February() {
      try {
          March();
      } catch (Ex1 ex) {
          System.out.println("February caught Ex1");
      } catch (Ex3 ex) {
          System.out.println("February caught Ex3");
      }
    }

    static void a() {
      try {
          February();
      } catch (Ex4 ex) {
          System.out.println("January caught Ex4");
          // now cause exception Ex1 to be thrown
      } catch (Ex1 ex) {
          System.out.println("January caught Ex1");
      }
    }

    public static void main(String[] args) {
        January();
    }
}

Assume now that this program is run four times. The first time, method e throws exception Ex1, the second time, it throws exception Ex2, etc.
What are the results of the four runs (a or b)?

And the answer is :

The program prints:
April caught Ex1
The program prints:
March caught Ex2
February caught Ex1
The program prints:
February caught Ex3
The program prints:
January caught Ex4
And execution stops due to an uncaught exception Ex1 thrown in main()

Can somebody tell me the explanation about this ?

Thank you

[JamesCherrill]

All you need to know is: it's optional to catch an unchecked exception; if you do catch it you execute whatever is in the catch block; if you don't catch it it is thrown back up to the method that called the current method. eg

When april calls e
   if e throws an exception it will be thrown back up to april because e does not catch it.
   if april gets an E1 it prints "April caught Ex1", all other exceptions are thrown back up to february.
   (etc)

That's all you ned to know to trace through all four cases yourself.