for(int x=0; x<10; x++, t += 0.5)
if(val < t) {
System.out.println("Average of values: " +
// display bell curve, sideways
for(int i=0; i<10; i++) {
for(int x=bell[i]; x>0; x--)
Here is a sample program run. As you can see, a bell-like distribution of numbers is obtained.
Average of values: 0.0702235271133344
Obser vable
The Observable class is used to create subclasses that other parts of your program can
observe. When an object of such a subclass undergoes a change, observing classes are
notified. Observing classes must implement the Observer interface, which defines the
update( ) method. The update( ) method is called when an observer is notified of a change
in an observed object.
Observable defines the methods shown in Table 18-7. An object that is being observed
must follow two simple rules. First, if it has changed, it must call setChanged( ). Second,
when it is ready to notify observers of this change, it must call notifyObservers( ). This
causes the update( ) method in the observing object(s) to be called. Be careful--if the object
calls notifyObservers( ) without having previously called setChanged( ), no action will take
place. The observed object must call both setChanged( ) and notifyObservers( ) before
update( ) will be called.
Notice that notifyObservers( ) has two forms: one that takes an argument and one that does
not. If you call notifyObservers( ) with an argument, this object is passed to the observer 's
update( ) method as its second parameter. Otherwise, null is passed to update( ). You can use
the second parameter for passing any type of object that is appropriate for your application.
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