1.
Write a short, simple scenario
to describe what happens when a caller tries to obtain a phone number by
calling Directory Enquiries, but the operator can’t find the number and has to
ask the caller to spell the name in order to find it. Draw a sequence diagram
to illustrate the scenario.
2.
Draw a statechart summarising
the information given in the following description of some of the events that
can arise in the life cycle of a thread in Java.
When a thread is created, it does not start running immediately, but is left in
the New Thread state. When the thread is in this state, it can only be
started or stopped. Calling any method besides start or stop
makes no sense, and causes an exception to be raised. The start method
causes system resources to be allocated to the thread, and calls the thread's run
method. At this point the thread is in the Running state. A thread
becomes not runnable if either its sleep or suspend methods
are called. The sleep method has a parameter specifying the length of
time the thread should sleep for; when this time has elapsed the thread starts
to run again. If the suspend method has been called, the thread only
runs again when its resume method is called. A thread can die in two
ways. It dies naturally when its run method exits normally. A thread
can also be killed at any time by calling its stop method.
3.
Consider a digital watch with
two buttons: A and B. When the watch is in the normal mode, pressing A toggles
the time display between 12 and 24 hour format, while pressing B illuminates
the watch display. If you keep A pressed for more than 3 seconds, then the
watch goes into set mode, which allows you to adjust the time. The adjustment
of the hours and the minutes takes place separately and you can toggle between
them by pressing the B button. The current selection is indicated by the
flashing of the respective part (i.e. the hours or minutes). In set mode
pressing button A increments the currently selected part by one. In order to
return to the normal mode the user needs to press A for more than 3 seconds.
When returning back into normal mode the watch displays time in the last used
format (12 or 24 hour). The adjustment of time is always in 24 hour format.
Construct a statechart representing the behaviour of the digital watch.