# Bounded Wildcards : Bounded Types « Generics « Java Tutorial

```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```
 12.5.Bounded Types 12.5.1. Bounded Types 12.5.2. Using Wildcard Arguments 12.5.3. Bounded Wildcards 12.5.4. Upper/lower bound for a wildcard