引言
原型是一种创建型设计模式， 使你能够复制对象， 甚至是复杂对象， 而又无需使代码依赖它们所属的类。
所有的原型类都必须有一个通用的接口， 使得即使在对象所属的具体类未知的情况下也能复制对象。 原型对象可以生成自身的完整副本， 因为相同类的对象可以相互访问对方的私有成员变量。
Java代码示例
使用示例： Java 的 Cloneable （可克隆） 接口就是立即可用的原型模式。
任何类都可通过实现该接口来实现可被克隆的性质。
java.lang.Object#clone() （类必须实现 java.lang.Cloneable 接口）
识别方法： 原型可以简单地通过 clone或 copy等方法来识别。
复制图形
让我们来看看在不使用标准 Cloneable接口的情况下如何实现原型模式。
shapes: 形状列表
shapes/Shape.java: 通用形状接口
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();@Overridepublic 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: 简单形状
public class Circle extends Shape {public int radius;public Circle() {}public Circle(Circle target) {super(target);if (target != null) {this.radius = target.radius;}}@Overridepublic Shape clone() {return new Circle(this);}@Overridepublic boolean equals(Object object2) {if (!(object2 instanceof Circle) || !super.equals(object2)) return false;Circle shape2 = (Circle) object2;return shape2.radius == radius;}
}shapes/Rectangle.java: 另一个形状
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;}}@Overridepublic Shape clone() {return new Rectangle(this);}@Overridepublic 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: 克隆示例
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: 执行结果
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!)原型注册站
你可以实现中心化的原型注册站 （或工厂）， 其中包含一系列预定义的原型对象。 这样一来， 你就可以通过传递对象名称或其他参数的方式从工厂处获得新的对象。 工厂将搜索合适的原型， 然后对其进行克隆复制， 最后将副本返回给你。
cache
cache/BundledShapeCache.java: 原型工厂
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: 克隆示例
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: 执行结果
Big green circle != Medium blue rectangle (yay!)
Medium blue rectangles are two different objects (yay!)
And they are identical (yay!)GO语言代码示例
概念示例
让我们尝试通过基于操作系统文件系统的示例来理解原型模式。 操作系统的文件系统是递归的： 文件夹中包含文件和文件夹， 其中又包含文件和文件夹， 以此类推。
每个文件和文件夹都可用一个 inode接口来表示。 inode接口中同样也有 clone克隆功能。
file文件和 folder文件夹结构体都实现了 print打印和 clone方法， 因为它们都是 inode类型。 同时， 注意 file和 folder中的 clone方法。 这两者的 clone方法都会返回相应文件或文件夹的副本。 同时在克隆过程中， 我们会在其名称后面添加 “_clone” 字样。
inode.go: 原型接口
package maintype Inode interface {print(string)clone() Inode
}file.go: 具体原型
package mainimport "fmt"type File struct {name string
}func (f *File) print(indentation string) {fmt.Println(indentation + f.name)
}func (f *File) clone() Inode {return &File{name: f.name + "_clone"}
}folder.go: 具体原型
package mainimport "fmt"type Folder struct {children []Inodename string
}func (f *Folder) print(indentation string) {fmt.Println(indentation + f.name)for _, i := range f.children {i.print(indentation + indentation)}
}func (f *Folder) clone() Inode {cloneFolder := &Folder{name: f.name + "_clone"}var tempChildren []Inodefor _, i := range f.children {copy := i.clone()tempChildren = append(tempChildren, copy)}cloneFolder.children = tempChildrenreturn cloneFolder
}main.go: 客户端代码
package mainimport "fmt"func main() {file1 := &File{name: "File1"}file2 := &File{name: "File2"}file3 := &File{name: "File3"}folder1 := &Folder{children: []Inode{file1},name: "Folder1",}folder2 := &Folder{children: []Inode{folder1, file2, file3},name: "Folder2",}fmt.Println("\nPrinting hierarchy for Folder2")folder2.print(" ")cloneFolder := folder2.clone()fmt.Println("\nPrinting hierarchy for clone Folder")cloneFolder.print(" ")
}output.txt: 执行结果
Printing hierarchy for Folder2Folder2Folder1File1File2File3Printing hierarchy for clone FolderFolder2_cloneFolder1_cloneFile1_cloneFile2_cloneFile3_cloneRuby代码示例
main.rb: 概念示例
# The example class that has cloning ability. We'll see how the values of field
# with different types will be cloned.
class Prototypeattr_accessor :primitive, :component, :circular_referencedef initialize@primitive = nil@component = nil@circular_reference = nilend# @return [Prototype]def clone@component = deep_copy(@component)# Cloning an object that has a nested object with backreference requires# special treatment. After the cloning is completed, the nested object# should point to the cloned object, instead of the original object.@circular_reference = deep_copy(@circular_reference)@circular_reference.prototype = selfdeep_copy(self)end# deep_copy is the usual Marshalling hack to make a deep copy. But it's rather# slow and inefficient, therefore, in real applications, use a special gemprivate def deep_copy(object)Marshal.load(Marshal.dump(object))end
endclass ComponentWithBackReferenceattr_accessor :prototype# @param [Prototype] prototypedef initialize(prototype)@prototype = prototypeend
end# The client code.
p1 = Prototype.new
p1.primitive = 245
p1.component = Time.now
p1.circular_reference = ComponentWithBackReference.new(p1)p2 = p1.cloneif p1.primitive == p2.primitiveputs 'Primitive field values have been carried over to a clone. Yay!'
elseputs 'Primitive field values have not been copied. Booo!'
endif p1.component.equal?(p2.component)puts 'Simple component has not been cloned. Booo!'
elseputs 'Simple component has been cloned. Yay!'
endif p1.circular_reference.equal?(p2.circular_reference)puts 'Component with back reference has not been cloned. Booo!'
elseputs 'Component with back reference has been cloned. Yay!'
endif p1.circular_reference.prototype.equal?(p2.circular_reference.prototype)print 'Component with back reference is linked to original object. Booo!'
elseprint 'Component with back reference is linked to the clone. Yay!'
endoutput.txt: 执行结果
Primitive field values have been carried over to a clone. Yay!
Simple component has been cloned. Yay!
Component with back reference has been cloned. Yay!
Component with back reference is linked to the clone. Yay!
