Java Reference
In-Depth Information
This case could slip past the compile-time checking if, for example, a referen-
ce to an array were stored in a variable of type
Object
.
• 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 recursive
application of these run-time rules for casting.
Example 5.5.3-1. Incompatible Types at Run Time
class Point { int x, y; }
interface Colorable { void setColor(int color); }
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);
}
}
This program uses casts to compile, but it throws exceptions at run time, because the
types are incompatible.
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
)
