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Proxy Pattern
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Define
proxy pattern
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Use a simple object to represent
a complex one or provide a placeholder for another object to control
access to it.
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Where
to use & benefits
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If creating an object is too
expensive in time or memory.
Postpone the creation until you need the actual object.
Load a large image (time consuming).
Load a remote object over network during peak periods.
Access right is required to a complex system.
Related patterns include
- Adapter pattern, which provides a different interface to
the object it adapts, whereas a proxy provides the same interface as
its subject, and
- Decorator pattern, which focuses on adding new functions to
an object, whereas a proxy controls access to the object.
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Example
of proxy pattern
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When loading a large image, you
may create some light object to represent it until the image is loaded
completely. Usually a proxy object has the same methods as the object
it represents. Once the object is loaded, it passes on the actual
object. For example,
abstract class Graphic {
public abstract void load();
public abstract void draw();
...
}
class Image extends Graphic{
public void load() {
...
}
public void draw() {
...
}
...
}
class ImgProxy extends Graphic {
public void load() {
if(image == null) {
image =
new Image(filename);
}
...
public void draw() {
...
}
...
}
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