The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
The following rules define a simple strategy for creating immutable objects. Not all classes documented as "immutable" follow these rules. This does not necessarily mean the creators of these classes were sloppy they may have good reason for believing that instances of their classes never change after construction. However, such strategies require sophisticated analysis and are not for beginners.
final
and private
.final
. A more sophisticated approach is to make the constructor private
and construct instances in factory methods.Applying this strategy to SynchronizedRGB
results in the following steps:
set
, arbitrarily transforms the object, and has no place in an immutable version of the class. The second one, invert
, can be adapted by having it create a new object instead of modifying the existing one.private
; they are further qualified as final
.final
.After these changes, we have
:ImmutableRGB
final public class ImmutableRGB { // Values must be between 0 and 255. final private int red; final private int green; final private int blue; final 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 ImmutableRGB(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 int getRGB() { return ((red << 16) | (green << 8) | blue); } public String getName() { return name; } public ImmutableRGB invert() { return new ImmutableRGB(255 - red, 255 - green, 255 - blue, "Inverse of " + name); } }