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Decorator Pattern - GUI Example - Java Sourcecode |
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Java Source Code Example for the Decorator Design Pattern - GUI Application
Decorator Design Pattern is applied in Graphical User Interface toolkits to add dynamically windows behaviors.
As discussed previously a persistence API can have many implementations depending on the presence or absence of a relational database, a file system, as well as on the underlying operating system.
The code below illustrates the Window interface representing the component interface.
package decorator;
/**
* Window Interface
*
* Component window
*/
public interface Window {
public void renderWindow();
}
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The code below illustrates concrete window implementation:
package decorator;
/**
* Window implementation
*
* Concrete implementation
*/
public class SimpleWindow implements Window {
@Override
public void renderWindow() {
// implementation of rendering details
}
}
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The code below illustrates the basic decorated window implementation. Note that the decorator maintains a reference to a window object that is being decorated.
package decorator;
/**
*
*/
public class DecoratedWindow implements Window{
/**
* private reference to the window being decorated
*/
private Window privateWindowRefernce = null;
public DecoratedWindow( Window windowRefernce) {
this.privateWindowRefernce = windowRefernce;
}
@Override
public void renderWindow() {
privateWindowRefernce.renderWindow();
}
}
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The code below illustrates a scrollable window which is a decorated window
package decorator;
/**
* Concrete Decorator with extended state
*
* Scrollable window creates a window that is scrollable
*
*
*/
public class ScrollableWindow extends DecoratedWindow{
/**
* Additional State
*/
private Object scrollBarObjectRepresentation = null;
public ScrollableWindow(Window windowRefernce) {
super(windowRefernce);
}
@Override
public void renderWindow() {
// render scroll bar
renderScrollBarObject();
// render decorated window
super.renderWindow();
}
private void renderScrollBarObject() {
// prepare scroll bar
scrollBarObjectRepresentation = new Object();
// render scrollbar
}
}
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The code below illustrates a driver program for the window component. Note how the scrolling functionality has been added dynamically at runtime.
package decorator;
public class GUIDriver {
public static void main(String[] args) {
// create a new window
Window window = new ConcreteWindow();
window.renderWindow();
// at some point later
// maybe text size becomes larger than the window
// thus the scrolling behavior must be added
// decorate old window
window = new ScrollableWindow(window);
// now window object
// has additional behavior / state
window.renderWindow();
}
}
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