Writing Scripts in Nashorn - Scripting in Java: Integrating with Groovy and JavaScript - page 112

print("Object.getPrototypeOf(point) === Object.prototype is " +
(Object.getPrototypeOf(point) === Object.prototype));
print("Object.getPrototypeOf(colorPoint) === point is " +
(Object.getPrototypeOf(coloredPoint) === point));
print("Object.getPrototypeOf(colorPoint) === Object.prototype is " +
(Object.getPrototypeOf(coloredPoint) === Object.prototype));

After setting the prototype for coloredPoint...
(10, 20)
(10, 20, red)
After setting the x and y properties for point...
(100, 200)
(100, 200, red)
[object Object]
[object Object]
Object.getPrototypeOf(point) === Object.prototype is true
Object.getPrototypeOf(colorPoint) === point is true
Object.getPrototypeOf(colorPoint) === Object.prototype is false

You can observe the following points in the code:

point object with three properties named x , y , • It defines a

and print

coloredPoint, with two
properties named color and print . At this point, the two objects
are unrelated.

• It defines another object, called

point object as the prototype of the coloredPoint
object using the Object.setPrototypeOf() function, so now
the coloredPoint object inherits from the point object. At this
point, the coloredPoint object inherits all properties of the
point object, including the properties x and y . Notice that only
one copy of x and y exists and they are shared by both point and
coloredPoint objects.

• It sets the

print() method on both objects. The output confirms
that both objects called their versions of the print() method.
This is a case of property overriding. The coloredPoint object
overrides the print() method of the point object. This works the
same as in Java.

• It calls the

x and y properties on the point
object and calls the print() method of both objects again. The
output confirms that the values of x and y were changed for both
point and coloredPoint objects.

• It changes the values for the