5.5

Casting Conversion

CONVERSIONS AND PROMOTIONS

O

If

T

 is an array type

TC[]

, that is, an array of components of type

TC

,

 then

a run time exception is thrown unless one of the following is true:

TC

 and

RC

 are the same primitive type.

TC

 and

RC

 are reference types and type

RC

 can be cast to

TC

 by a recur 

sive application of these run time rules for casting.

If a run time exception is thrown, it is a

ClassCastException

 ( 11.5.1.1,

 20.22).

Here are some examples of casting conversions of reference types, similar to

the example in  5.2:

public class Point { int x, y; }

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

public class ColoredPoint extends Point implements Colorable

{

int color;

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

}

final class EndPoint extends Point { }

class Test {

public static void main(String[] args) {

Point p = new Point();

ColoredPoint cp = new ColoredPoint();

Colorable c;

//

The following may cause errors at run time because

//

we cannot be sure they will succeed; this possibility

//

is suggested by the casts:

cp = (ColoredPoint)p; // p

 might not reference an

//

object which is a

ColoredPoint

//

or a subclass of

ColoredPoint

c = (Colorable)p;

// p

 might not be

Colorable

//

The following are incorrect at compile time because

//

they can never succeed as explained in the text:

Long l = (Long)p;

//

compile time error #1

EndPoint e = new EndPoint();

c = (Colorable)e;

//

compile time error #

2

}

}

Here the first compile time error occurs because the class types

Long

 and

Point

are unrelated (that is, they are not the same, and neither is a subclass of the other),

so a cast between them will always fail.

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