To create a generic sameAvg( ) method, you must use another feature of Java generics:
the wildcard argument. The wildcard argument is specified by the ?, and it represents an
unknown type. Using a wildcard, here is one way to write the sameAvg( ) method:
// Determine if two averages are the same.
// Notice the use of the wildcard.
boolean sameAvg(Stats<?> ob) {
if(average() == ob.average())
return true;
return false;
}
Here, Stats<?> matches any Stats object, allowing any two Stats objects to have their
averages compared. The following program demonstrates this:
// Use a wildcard.
class Stats<T extends Number> {
T[] nums; // array of Number or subclass
// Pass the constructor a reference to
// an array of type Number or subclass.
Stats(T[] o) {
nums = o;
}
// Return type double in all cases.
double average() {
double sum = 0.0;
for(int i=0; i < nums.length; i++)
sum += nums[i].doubleValue();
return sum / nums.length;
}
// Determine if two averages are the same.
// Notice the use of the wildcard.
boolean sameAvg(Stats<?> ob) {
if(average() == ob.average())
return true;
return false;
}
}
// Demonstrate wildcard.
class WildcardDemo {
public static void main(String args[]) {
Integer inums[] = { 1, 2, 3, 4, 5 };
Stats<Integer> iob = new Stats<Integer>(inums);
double v = iob.average();
System.out.println("iob average is " + v);
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