GenericsBounded.java

// In this version of NumericFns, the type argument for T
// must be either Number, or a class derived from Number.
class NumericFns<T extends Number> {
    T num;

    // Pass the constructor a reference to a numeric object.
    NumericFns(T n) {
        num = n;
    }

    // Return the reciprocal.
    double reciprocal() {
        return 1 / num.doubleValue();
    }

    // Return the fractional component.
    double fraction() {
        return num.doubleValue() - num.intValue();
    }
}

public class GenericsBounded {
    public static void main(String[] args) {
        NumericFns<Integer> iOb =
                new NumericFns<Integer>(5);
        System.out.println("Reciprocal of iOb is " +
                iOb.reciprocal());
        System.out.println("Fractional component of iOb is " +
                iOb.fraction());
        System.out.println();
        NumericFns<Double> dOb =
                new NumericFns<Double>(5.25);
        System.out.println("Reciprocal of dOb is " +
                dOb.reciprocal());
        System.out.println("Fractional component of dOb is " +
                dOb.fraction());
        // This won't compile because String is not a
        // subclass of Number.
        // NumericFns<String> strOb = new NumericFns<String>("Error");
    }
}