5.6

Numeric Promotions

CONVERSIONS AND PROMOTIONS

The following example uses casts to compile, but it throws exceptions at run

time, because the types are incompatible:

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; }

}

class Test {

public static void main(String[] args) {

Point[] pa = new Point[100];

//

The following line will throw a

ClassCastException

:

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

System.out.println(cpa[0]);

int[] shortvec = new int[2];

Object o = shortvec;

//

The following line will throw a

ClassCastException

:

Colorable c = (Colorable)o;

c.setColor(0);

}

}

5.6   Numeric Promotions

Numeric promotion

 is applied to the operands of an arithmetic operator. Numeric

promotion contexts allow the use of an identity conversion ( 5.1.1) or a widening

primitive conversion ( 5.1.2).

Numeric promotions are used to convert the operands of a numeric operator to

a common type so that an operation can be performed. The two kinds of numeric

promotion are unary numeric promotion ( 5.6.1) and binary numeric promotion

( 5.6.2). The analogous conversions in C are called  the usual unary conversions 

and  the usual binary conversions. 

Numeric promotion is not a general feature of Java, but rather a property of

the specific definitions of the built in operations.

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