Definition: The Proxy pattern provides a placeholder for another object to gain access to it.

Usage: A remote proxy controls access to a remote object. A virtual proxy controls access to a resource that is expensive to create. A protection proxy controls access to a resource based on access rights.

Example

interface WidgetlessRenderer {
	void drawTo(Graphics2D g2, int x, int y, int width, int height)
}

class ImageRendererProxy implements WidgetlessRenderer {
	ImageRendererProxy(Url url) {
		start loading image from url
	}

	void drawTo(Graphics2D g2, int x, int y, int width, int height) {
		if image is done loading
			display the image
		else
			display the text "Loading Image..."
	}
}

This class allows an image placeholder to be displayed before the image is fully loaded. This used to be standard in applets because modems couldn't download images fast enough.