proxy.go

package main

import "fmt"

type Image interface {
	DisplayImage()
}

type RealImage struct {
	fileImage string
}

func NewRealImage(fileName string) *RealImage {
	return &RealImage{fileName}
}

func (self *RealImage) DisplayImage() {
	fmt.Println("Display ", self.fileImage)
}

type ProxyImage struct {
	fileName string
	image    Image
}

func NewProxyImage(fileName string) *ProxyImage {
	return &ProxyImage{fileName, nil}
}

func (self *ProxyImage) DisplayImage() {
	if self.image == nil {
		self.image = NewRealImage(self.fileName)
	}
	self.image.DisplayImage()
}

func main() {
	image1 := NewProxyImage("HiRes_10MB_Photo1")
	image2 := NewProxyImage("HiRes_10MB_Photo2")

	image1.DisplayImage()
	image2.DisplayImage()
	image2.DisplayImage()
}