Activity 4.4 - A program which throws an exception

Topic

In this activity, we witness a Java exception being thrown in a fairly spectacular manner.

Materials

In addition to the Solution document, the project for this activity contains two classes:

• GreedyClass, containing a method grabSomeMemory(int n) that tries to allocate enough memory for an array of int variables with n elements (i.e. 4*n bytes);
• Main, which creates an instance of the GreedyClass class and invokes a method, requesting an amount of memory that is likely to be absurd, at least at the time of writing!

Instructions

1. Run the project. You will find the program halts and reports an exception. Normally, exceptions result in messages that are quite informative, but this case is possibly a bit extreme, so we don't get told too much!
2. Confirm that this exception does not occur for more modest memory allocation requests. In the main method of Main, decrease the amount of memory requested by a factor of 1000, like this:

   final int AMOUNT = 1000*1000;

   Run the project again - you should find that it completes successfully.

3. Just for interest, in the main method of Main, try the effect of attempting to increase the amount of memory requested by a factor of 1000 compared to the original program, like this:

   final int AMOUNT = 1000*1000*1000*1000;

   What happens this time?