Prototype en Java
Le Prototype est un patron de conception de création qui permet de cloner des objets - même complexes - sans se coupler à leur classe.
Toutes les classes prototype devraient avoir une interface commune rendant possible la copie des objets, même sans connaître leur classe concrète. Les objets prototype peuvent créer des copies complètes puisqu’ils peuvent accéder aux attributs privés des autres objets de la même classe.
Complexité :
Popularité :
Exemples d’utilisation : Le prototype est prêt à l’emploi dans Java avec une interface Cloneable.
N’importe quelle classe peut implémenter cette interface pour devenir clonable.
- (La classe
java.lang.Object#clone()devrait implémenter l’interfacejava.lang.Cloneable)
Identification : Le prototype peut facilement être reconnu grâce aux méthodes clone, copier, etc.
Copier des formes graphiques
Regardons comment le prototype peut être implémenté sans l’interface standard Cloneable.
shapes: Liste des formes
shapes/Shape.java: Interface Forme commune
package refactoring_guru.prototype.example.shapes;
import java.util.Objects;
public abstract class Shape {
public int x;
public int y;
public String color;
public Shape() {
}
public Shape(Shape target) {
if (target != null) {
this.x = target.x;
this.y = target.y;
this.color = target.color;
}
}
public abstract Shape clone();
@Override
public boolean equals(Object object2) {
if (!(object2 instanceof Shape)) return false;
Shape shape2 = (Shape) object2;
return shape2.x == x && shape2.y == y && Objects.equals(shape2.color, color);
}
}
shapes/Circle.java: Forme simple
package refactoring_guru.prototype.example.shapes;
public class Circle extends Shape {
public int radius;
public Circle() {
}
public Circle(Circle target) {
super(target);
if (target != null) {
this.radius = target.radius;
}
}
@Override
public Shape clone() {
return new Circle(this);
}
@Override
public boolean equals(Object object2) {
if (!(object2 instanceof Circle) || !super.equals(object2)) return false;
Circle shape2 = (Circle) object2;
return shape2.radius == radius;
}
}
shapes/Rectangle.java: Une autre forme
package refactoring_guru.prototype.example.shapes;
public class Rectangle extends Shape {
public int width;
public int height;
public Rectangle() {
}
public Rectangle(Rectangle target) {
super(target);
if (target != null) {
this.width = target.width;
this.height = target.height;
}
}
@Override
public Shape clone() {
return new Rectangle(this);
}
@Override
public boolean equals(Object object2) {
if (!(object2 instanceof Rectangle) || !super.equals(object2)) return false;
Rectangle shape2 = (Rectangle) object2;
return shape2.width == width && shape2.height == height;
}
}
Demo.java: Exemple de clonage
package refactoring_guru.prototype.example;
import refactoring_guru.prototype.example.shapes.Circle;
import refactoring_guru.prototype.example.shapes.Rectangle;
import refactoring_guru.prototype.example.shapes.Shape;
import java.util.ArrayList;
import java.util.List;
public class Demo {
public static void main(String[] args) {
List<Shape> shapes = new ArrayList<>();
List<Shape> shapesCopy = new ArrayList<>();
Circle circle = new Circle();
circle.x = 10;
circle.y = 20;
circle.radius = 15;
circle.color = "red";
shapes.add(circle);
Circle anotherCircle = (Circle) circle.clone();
shapes.add(anotherCircle);
Rectangle rectangle = new Rectangle();
rectangle.width = 10;
rectangle.height = 20;
rectangle.color = "blue";
shapes.add(rectangle);
cloneAndCompare(shapes, shapesCopy);
}
private static void cloneAndCompare(List<Shape> shapes, List<Shape> shapesCopy) {
for (Shape shape : shapes) {
shapesCopy.add(shape.clone());
}
for (int i = 0; i < shapes.size(); i++) {
if (shapes.get(i) != shapesCopy.get(i)) {
System.out.println(i + ": Shapes are different objects (yay!)");
if (shapes.get(i).equals(shapesCopy.get(i))) {
System.out.println(i + ": And they are identical (yay!)");
} else {
System.out.println(i + ": But they are not identical (booo!)");
}
} else {
System.out.println(i + ": Shape objects are the same (booo!)");
}
}
}
}
OutputDemo.txt: Résultat de l’exécution
0: Shapes are different objects (yay!)
0: And they are identical (yay!)
1: Shapes are different objects (yay!)
1: And they are identical (yay!)
2: Shapes are different objects (yay!)
2: And they are identical (yay!)
Registre de prototypes
Vous pouvez implémenter un registre de prototypes centralisé (ou fabrique) qui contiendrait un ensemble d’objets prototype prédéfinis. Ainsi vous pouvez récupérer de nouveaux objets de la fabrique en passant leur nom ou d’autres paramètres. La fabrique chercherait le prototype approprié, le clonerait et vous enverrait une copie.
cache
cache/BundledShapeCache.java: Fabrique de prototypes
package refactoring_guru.prototype.caching.cache;
import refactoring_guru.prototype.example.shapes.Circle;
import refactoring_guru.prototype.example.shapes.Rectangle;
import refactoring_guru.prototype.example.shapes.Shape;
import java.util.HashMap;
import java.util.Map;
public class BundledShapeCache {
private Map<String, Shape> cache = new HashMap<>();
public BundledShapeCache() {
Circle circle = new Circle();
circle.x = 5;
circle.y = 7;
circle.radius = 45;
circle.color = "Green";
Rectangle rectangle = new Rectangle();
rectangle.x = 6;
rectangle.y = 9;
rectangle.width = 8;
rectangle.height = 10;
rectangle.color = "Blue";
cache.put("Big green circle", circle);
cache.put("Medium blue rectangle", rectangle);
}
public Shape put(String key, Shape shape) {
cache.put(key, shape);
return shape;
}
public Shape get(String key) {
return cache.get(key).clone();
}
}
Demo.java: Exemple de clonage
package refactoring_guru.prototype.caching;
import refactoring_guru.prototype.caching.cache.BundledShapeCache;
import refactoring_guru.prototype.example.shapes.Shape;
public class Demo {
public static void main(String[] args) {
BundledShapeCache cache = new BundledShapeCache();
Shape shape1 = cache.get("Big green circle");
Shape shape2 = cache.get("Medium blue rectangle");
Shape shape3 = cache.get("Medium blue rectangle");
if (shape1 != shape2 && !shape1.equals(shape2)) {
System.out.println("Big green circle != Medium blue rectangle (yay!)");
} else {
System.out.println("Big green circle == Medium blue rectangle (booo!)");
}
if (shape2 != shape3) {
System.out.println("Medium blue rectangles are two different objects (yay!)");
if (shape2.equals(shape3)) {
System.out.println("And they are identical (yay!)");
} else {
System.out.println("But they are not identical (booo!)");
}
} else {
System.out.println("Rectangle objects are the same (booo!)");
}
}
}
OutputDemo.txt: Résultat de l’exécution
Big green circle != Medium blue rectangle (yay!)
Medium blue rectangles are two different objects (yay!)
And they are identical (yay!)
