MODULE 2p - Exception Throwing and Catching

FIRST TASK

Key in and try out the  ArgsArrayA  program and note that the
ArrayIndexOutOfBoundsException  is thrown when there are fewer
than three arguments.


SECOND TASK

To stop the program crashing when an exception is thrown the
appropriate course of action is to embed the statement or
statements that might throw the exception in a try-clause
and then catch the exception, including helpful println
statements in an associated catch-clause.  Modify ArgsArrayA
to...

public class ArgsArrayEx
 { public static void main(String[] args)
    { System.out.println("There are " + args.length + " arguments");
      try
       { System.out.println(args[0] + " " + args[1] + " " + args[2]);
       }
      catch(ArrayIndexOutOfBoundsException e)
       { System.out.println("Reading non-existent array element");
       }
    }
 }

Test this program with three arguments and no arguments.


THIRD TASK

Key in the following program in which  Thread.sleep(3000L);  is
supposed to pause the program for 3000 milliseconds.  The L in
the argument 3000L indicates a long integer (64-bit) constant.

public class HelloA
 { public static void main(String[] args)
    { System.out.println("Hello");
      Thread.sleep(3000L);
      System.out.println("World");
    }
 }

This program won't compile.  The compiler complains:

HelloA.java:4: Exception java.lang.InterruptedException
must be caught, or it must be declared in the throws clause
of this method.

Thread.sleep(3000L);
            ^
1 error


FOURTH TASK

Embed  Thread.sleep(3000L);  in a try-clause and catch the
InterruptedException  as in the following...

public class HelloB
 { public static void main(String[] args)
    { System.out.println("Hello");
      try
       { Thread.sleep(3000L);
       }
      catch (InterruptedException e)
       { System.out.println("Interrupted while asleep");
       }
      System.out.println("World");
    }
 }

Compile and run this program.