The class,, 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.
SynchronizedRGB
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:If another thread invokesSynchronizedRGB color = new SynchronizedRGB(0, 0, 0, "Pitch Black"); ... int myColorInt = color.getRGB(); //Statement 1 String myColorName = color.getName(); //Statement 2color.set
after Statement 1 but before Statement 2, the value ofmyColorInt
won't match the value ofmyColorName
. To avoid this outcome, the two statements must be bound together:This kind of inconsistency is only possible for mutable objects — it will not be an issue for the immutable version ofsynchronized (color) { int myColorInt = color.getRGB(); String myColorName = color.getName(); }SynchronizedRGB
.