Functions and Recursive Functions - A Concise and Practical Introduction to Programming Algorithms in Java - page 63

accessed from outside the function bodies.
Suppose now that we would like to count the number of times a given function
is called. We need to declare a kind of persistent variable that we can attach
to the class encapsulating the function: These kinds of persistent variables are
called static variables. Using static variables, it becomes easy, say, to count the
overall number of function calls as illustrated by the following code:

Program 3.5 An example using a static (class) variable
class StaticVariable {
static int nbfunccalls=0;

static int square( int x)
{ nbfunccalls++;
return x ∗ x; }

static boolean isOdd( int p)
{ nbfunccalls++;
if ( ( p%2)==0) return false ;
else return true ; }

static double distance( double x, double y)
{ double result ;
nbfunccalls++;
if (x > y) result=x − y;

else result=y − x;

return result ;
}

static void display( double x, double y)
{ nbfunccalls++;
System . out . println ( "(" +x+ "," +y+ ")" );
}

public static void main ( String [ ] args )

{ FunctionDeclaration . display (3 ,2) ;
display(square(2) ,distance (5 ,9)) ;

int p=123124345;
if (isOdd(p) )
System . out . println ( "p is odd" );
else System . out . println ( "p is even" );

System . out . println ( "Total number of function calls:" +
nbfunccalls) ;

}

}

Running this program, we get the following message after completion:
Total number of function calls:4