代理模式：创建真实对象的效率如何？

通过您发布的链接（重点是我的）：

代理类ProxyImage在真实图像类本身之外的其他系统上运行，并且可以在该系统上表示真实图像RealImage。可从磁盘访问映像信息。使用代理模式，的代码ProxyImage 避免了多次加载图像，从而以节省内存的方式从其他系统访问该图像。

简而言之：它不节省内存，它可以加快应用程序的速度，因为您不需要每次都访问磁盘来读取真实图像。

这在代码的这一部分中得到了证明：

public void displayImage() {
    //if image is not loaded into memory
    if (image == null) {
        //then load it, go to disk only once
        image = new RealImage(filename);
    }
    //now it is in memory, display the real image
    image.displayImage();
}

为了更好地理解此问题，让我们更改类和接口的定义：

public interface Image {
    String getName();
    byte[] getData();
}

现在，RealImage该类将始终在磁盘中寻找数据，以防文件不存在（文件被删除或重命名）：

public class RealImage implements Image {
    //implements all the operations going to disk...
    private String fileName;
    public RealImage(String fileName) {
        this.fileName = fileName;
    }
    @Override
    public String getName() {
        String name = "";
        //fancy operations to seek for the file in disk (in case it has been deleted)
        //read the data from file in disk
        //get the name
        name = ...;
        return name;
    }
    @Override
    public byte[] getData() {
        byte[] data;
        //again, fancy operations to seek for the file in disk (in case it has been deleted)
        //read the data from file in disk
        //get the image data for displaying purposes
        data = ...;
        return data;
    }
}

现在，我们的商品ProxyImage将充当代理，RealImage通过将数据保存到内存中来节省每次昂贵的磁盘任务：

public class ProxyImage implements Image {
    private String fileName;
    private RealImage realImage;
    private byte[] data;
    private String name;
    //implements all the operations going to disk...
    public RealImage(String fileName) {
        this.fileName = fileName;
    }
    @Override
    public String getName() {
        //in case we don't have the name of the image
        if (this.name == null) {
            //use a RealImage to retrieve the image name
            //we will create the instance of realImage only if needed
            if (realImage == null) {
                realImage = new RealImage(fileName);
            }
            //getting the image from the real image is highly costly
            //so we will do this only once
            this.name = realImage.getName();
        }
        return this.name;
    }
    @Override
    public byte[] getData() {
        //similar behavior for the data of the image
        if (this.data == null) {
            if (realImage == null) {
                realImage = new RealImage(fileName);
            }
            //highly costly operation
            this.data = realImage.getData();
        }
        return this.data;
    }
}

因此反映了为我们的代理使用代理的好处RealImage。