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🔔 Subscribe to Ram N JavaUnderstanding the Virtual Proxy Design Pattern
The Virtual Proxy Pattern is a specialized implementation of the Proxy structural design pattern. It acts as a placeholder for resource-intensive or heavyweight objects, delaying their creation and initialization until they are genuinely needed (a concept known as lazy loading or lazy initialization).
Why Use a Virtual Proxy?
Creating complex objects upfront—such as high-resolution images, large data models, or external service connections—can severely degrade performance and consume heavy memory. A Virtual Proxy solves this problem by:
- Providing the exact same interface as the real subject.
- Handling lightweight operations without loading the real object.
- Instantiating the expensive object only when an essential operation is requested.
Key Components of Virtual Proxy
- Subject Interface: Declares common operations for both the real object and the proxy.
- Real Subject: The actual heavyweight object that performs the core, memory-intensive work.
- Virtual Proxy: Holds a reference to the real subject, controlling its instantiation and access transparently.
Explore More Proxy Pattern Tutorials
Expand your understanding of proxy architectures with these related tutorials from our channel:
Click here to watch in Youtube : https://www.youtube.com/watch?v=ooPPd_LIkzQ
Click the below Image to Enlarge
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| Virtual Proxy |
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| Virtual Proxy - Class Diagram |
Image.java
interface Image
{
public void displayImage();
}
RealImage.java
//on System A
class RealImage implements Image
{
private String filename = null;
/**
* Constructor
*
* @param FILENAME
*/
public RealImage( final String FILENAME )
{
filename = FILENAME;
loadImageFromDisk();
}
/**
* Loads the image from the disk
*/
private void loadImageFromDisk()
{
System.out.println(" Loading " + filename);
}
/**
* Displays the image
*/
public void displayImage()
{
System.out.println(" Displaying " + filename+"\n");
}
}
ProxyImage.java
//on System B
class ProxyImage implements Image
{
private RealImage image = null;
private String filename = null;
/**
* Constructor
*
* @param FILENAME
*/
public ProxyImage( final String FILENAME )
{
filename = FILENAME;
}
/**
* Displays the image
*/
public void displayImage()
{
if( image == null )
{
image = new RealImage(filename);
}
image.displayImage();
}
}
Client.java
class Client
{
/**
* Test method
*/
public static void main( String[] args )
{
final Image IMAGE1 = new ProxyImage("HiResolution_100MB_Dog Photo");
final Image IMAGE2 = new ProxyImage("HiResolution_100MB_Lion photo");
System.out.println("IMAGE1["+IMAGE1+"] calling displayImage first time :");
IMAGE1.displayImage(); // loading necessary
System.out.println("IMAGE1["+IMAGE1+"] calling displayImage second time :");
IMAGE1.displayImage(); // loading unnecessary
System.out.println("IMAGE1["+IMAGE1+"] calling displayImage third time :");
IMAGE1.displayImage(); // loading unnecessary
System.out.println("###############################################################\n");
System.out.println("IMAGE2["+IMAGE2+"] calling displayImage first time :");
IMAGE2.displayImage(); // loading necessary
System.out.println("IMAGE2["+IMAGE2+"] calling displayImage second time :");
IMAGE2.displayImage(); // loading unnecessary
}
}
Output
IMAGE1[ProxyImage@1ad086a] calling displayImage first time :
Loading HiResolution_100MB_Dog Photo
Displaying HiResolution_100MB_Dog Photo
IMAGE1[ProxyImage@1ad086a] calling displayImage second time :
Displaying HiResolution_100MB_Dog Photo
IMAGE1[ProxyImage@1ad086a] calling displayImage third time :
Displaying HiResolution_100MB_Dog Photo
###############################################################
IMAGE2[ProxyImage@42719c] calling displayImage first time :
Loading HiResolution_100MB_Lion photo
Displaying HiResolution_100MB_Lion photo
IMAGE2[ProxyImage@42719c] calling displayImage second time :
Displaying HiResolution_100MB_Lion photo
See also:
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