The class,
SynchronizedRGB, defines objects that represent colors. Each object represents the
color as three integers that stand for primary color values and a
string that gives the name of the color.
public class SynchronizedRGB {
//Values must be between 0 and 255.
private int red;
private int green;
private int blue;
private String name;
private void check(int red, int green, int blue) {
if (red < 0 || red > 255
|| green < 0 || green > 255
|| blue < 0 || blue > 255) {
throw new IllegalArgumentException();
}
}
public SynchronizedRGB(int red, int green, int blue, String name) {
check(red, green, blue);
this.red = red;
this.green = green;
this.blue = blue;
this.name = name;
}
public void set(int red, int green, int blue, String name) {
check(red, green, blue);
synchronized (this) {
this.red = red;
this.green = green;
this.blue = blue;
this.name = name;
}
}
public synchronized int getRGB() {
return ((red << 16) | (green << 8) | blue);
}
public synchronized String getName() {
return name;
}
public synchronized void invert() {
red = 255 - red;
green = 255 - green;
blue = 255 - blue;
name = "Inverse of " + name;
}
}
SynchronizedRGB must be used carefully to avoid being
seen in an inconsistent state. Suppose, for example, a thread executes
the following code:
SynchronizedRGB color = new SynchronizedRGB(0, 0, 0, "Pitch Black");
...
int myColorInt = color.getRGB(); //Statement 1
String myColorName = color.getName(); //Statement 2
If another thread invokes
color.set after Statement 1
but before Statement 2, the value of
myColorInt won't
match the value of
myColorName. To avoid this outcome,
the two statements must be bound together:
synchronized (color) {
int myColorInt = color.getRGB();
String myColorName = color.getName();
}
This kind of inconsistency is only possible for mutable objects
— it will not be an issue for the immutable version of
SynchronizedRGB.
