设计模式（9）——Decorator(装饰）模式

矫情吗；* 2022-08-08 06:39 176阅读 0赞

### 什么是装饰模式？ ###

装饰模式是动态地（在运行时）给一个对象添加一些额外的职责。

![Image 1][]

### 装饰模式的适用范围 ###

1.在不影响其他对象的情况下，以动态、透明的方式给单个对象添加职责；

2. 处理那些可以撤销的职责

3. 当不能采用生成子类的方式进行扩充时。

### 装饰模式的示例 ###

![Image 1][]

/**
     * Window Interface 
     * 
     * Component window
     */
    public interface Window {
    
    	public void renderWindow();
    	
    }

/**
     * Window implementation 
     * 
     * Concrete implementation
     */
    public class SimpleWindow implements Window {
    
    	@Override
    	public void renderWindow() {
    		// implementation of rendering details
    
    	}
    }

/**
     *
     */
    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();
    		
    	}
    }

/**
     * 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 
    		
    	}	
    }

[Image 1]: