How to create Immutable Objects

A Strategy for Defining Immutable Objects

 

 

·  Don't provide "setter" methods — methods that modify fields or objects referred to by fields.

·  Make all fields final and private.

·  Don't allow subclasses to override methods. The simplest way to do this is to declare the class as final. A more sophisticated approach is to make the constructor private and construct instances in factory methods.

 

Eg Code here:

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;

    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;

    }

}