Java Reference
In-Depth Information
this.color = (byte)color;
}
/** Copy all relevant fields of the argument into
this ColoredPoint object. */
public void adopt(Point p) { x = p.x; y = p.y; }
public String toString() {
String s = "," + COLORS[color];
return super.toString(s);
}
}
Now consider a third compilation unit that uses
ColoredPoint
:
import points.*;
class Test {
public static void main(String[] args) {
ColoredPoint cp =
new ColoredPoint(6, 6, ColoredPoint.RED);
ColoredPoint cp2 =
new ColoredPoint(3, 3, ColoredPoint.GREEN);
cp.adopt(cp2);
System.out.println("cp: " + cp);
}
}
The output is:
cp: (3,3,red)
The programmer who coded class
Test
has expected to see the word
green
, because the
actual argument, a
ColoredPoint
, has a
color
field, and
color
would seem to be a “relevant
field”. (Of course, the documentation for the package
points
ought to have been much
more precise!)
Notice, by the way, that the most specific method (indeed, the only applicable method)
for the method invocation of
adopt
has a signature that indicates a method of one para-
meter, and the parameter is of type
Point
. This signature becomes part of the binary
representation of class
Test
produced by the Java compiler and is used by the method
invocation at run time.
Suppose the programmer reported this software error and the maintainer of the
points
package decided, after due deliberation, to correct it by adding a method to class
Co-
loredPoint
:
public void adopt(ColoredPoint p) {
