CONVERSIONS AND PROMOTIONS

Casting Conversion

5.5

The second compile time error occurs because a variable of type

EndPoint

can never reference a value that implements the interface

Colorable

. This is

because

EndPoint

 is a

final

 type, and a variable of a

final

 type always holds a

value of the same run time type as its compile time type. Therefore, the run time

type of variable

e

 must be exactly the type

EndPoint

, and type

EndPoint

 does

not implement

Colorable

.

Here is an example involving arrays ( 10):

class Point {

int x, y;

Point(int x, int y) { this.x = x; this.y = y; }

public String toString() { return "("+x+","+y+")"; }

}

public interface Colorable { void setColor(int color); }

public class ColoredPoint extends Point implements Colorable

{

int color;

ColoredPoint(int x, int y, int color) {

super(x, y); setColor(color);

}

public void setColor(int color) { this.color = color; }

public String toString() {

return super.toString() + "@" + color;

}

}

class Test {

public static void main(String[] args) {

Point[] pa = new ColoredPoint[4];

pa[0] = new ColoredPoint(2, 2, 12);

pa[1] = new ColoredPoint(4, 5, 24);

ColoredPoint[] cpa = (ColoredPoint[])pa;

System.out.print("cpa: {");

for (int i = 0; i < cpa.length; i++)

System.out.print((i == 0 ? " " : ", ") + cpa[i]);

System.out.println(" }");

}

}

This example compiles without errors and produces the output:

cpa: { (2,2)@12, (4,5)@24, null, null }

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