Mega Code Archive
Bounded Wildcards
<![CDATA[
class Two {
int x, y;
Two(int a, int b) {
x = a;
y = b;
}
}
class Three extends Two {
int z;
Three(int a, int b, int c) {
super(a, b);
z = c;
}
}
class Four extends Three {
int t;
Four(int a, int b, int c, int d) {
super(a, b, c);
t = d;
}
}
class Gen<T extends Two> {
T[] coords;
Gen(T[] o) {
coords = o;
}
}
// Demonstrate a bounded wildcard.
public class MainClass {
static void showTwo(Gen<?> c) {
System.out.println("X Y Coordinates:");
for (int i = 0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " + c.coords[i].y);
System.out.println();
}
static void showThree(Gen<? extends Three> c) {
System.out.println("X Y Z Coordinates:");
for (int i = 0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " + c.coords[i].y + " " + c.coords[i].z);
System.out.println();
}
static void showAll(Gen<? extends Four> c) {
System.out.println("X Y Z T Coordinates:");
for (int i = 0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " + c.coords[i].y + " " + c.coords[i].z + " "
+ c.coords[i].t);
System.out.println();
}
public static void main(String args[]) {
Two td[] = { new Two(0, 0), new Two(7, 9), new Two(18, 4), new Two(-1, -23) };
Gen<Two> tdlocs = new Gen<Two>(td);
System.out.println("Contents of tdlocs.");
showTwo(tdlocs); // OK, is a TwoD
Four fd[] = { new Four(1, 2, 3, 4), new Four(6, 8, 14, 8), new Four(22, 9, 4, 9),
new Four(3, -2, -23, 17) };
Gen<Four> fdlocs = new Gen<Four>(fd);
System.out.println("Contents of fdlocs.");
// These are all OK.
showTwo(fdlocs);
showThree(fdlocs);
showAll(fdlocs);
}
}
Contents of tdlocs.
X Y Coordinates:
0 0
7 9
18 4
-1 -23
Contents of fdlocs.
X Y Coordinates:
1 2
6 8
22 9
3 -2
X Y Z Coordinates:
1 2 3
6 8 14
22 9 4
3 -2 -23
X Y Z T Coordinates:
1 2 3 4
6 8 14 8
22 9 4 9
3 -2 -23 17
]]>