装饰器设计模式

装饰者模式说, 只是“将灵活的附加职责动态地附加到对象上”。

换句话说, 装饰器模式使用合成而不是继承来扩展对象在运行时的功能。

装饰器模式也称为包装器。

装饰图案的优势

• 它提供了比静态继承更大的灵活性。
• 因为可以通过对新类进行编码来进行更改, 所以可以增强对象的可扩展性。
• 它允许你从目标类开发一系列功能, 而不是将所有行为编码到对象中, 从而简化了编码。

装饰图案的用法

它用于：

• 当你想要透明, 动态地向对象添加职责而又不影响其他对象时。
• 当你想向对象添加职责时, 将来可能需要更改。
• 通过子类扩展功能不再可行。

用于装饰器模式的UML：

第1步：创建食物界面。

public interface Food {
	public String prepareFood();
	public double foodPrice();
}// End of the Food interface.

步骤2：创建一个VegFood类, 该类将实现Food接口并覆盖其所有方法。

public class VegFood implements Food {
	public String prepareFood(){
		 return "Veg Food";
	}

        public double foodPrice(){
		return 50.0;
	}
}

第3步：创建一个FoodDecorator抽象类, 该类将实现Food接口并覆盖所有方法, 并且可以装饰更多食物。

public abstract class FoodDecorator implements Food{
	private Food newFood;
	public FoodDecorator(Food newFood)	{
		this.newFood=newFood;
	}
	@Override
	public String prepareFood(){
		return newFood.prepareFood(); 
	}
	public double foodPrice(){
		return newFood.foodPrice();
	}
}

步骤4：创建NonVegFood具体类, 该类将扩展FoodDecorator类并覆盖所有方法。

public class NonVegFood extends FoodDecorator{	
	public NonVegFood(Food newFood) {
		super(newFood);
	}
	public String prepareFood(){
		return super.prepareFood() +" With Roasted Chiken and Chiken Curry  "; 
	}
	public double foodPrice()	{
		return super.foodPrice()+150.0;
	}
}

第5步：创建一个ChineeseFood具体类, 该类将扩展FoodDecorator类并覆盖所有方法。

public class ChineeseFood extends FoodDecorator{
  public ChineeseFood(Food newFood)    {
		super(newFood);
  }
	public String prepareFood(){
		return super.prepareFood() +" With Fried Rice and Manchurian  "; 
	}
	public double foodPrice()	{
		return super.foodPrice()+65.0;
        }
}

步骤6：创建一个DecoratorPatternCustomer类, 该类将使用Food接口来使用客户想要的食物类型（Decorates）。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class DecoratorPatternCustomer {
	private static int  choice;
	public static void main(String args[]) throws NumberFormatException, IOException	{
       do{		
		System.out.print("========= Food Menu ============ \n");
		System.out.print("            1. Vegetarian Food.   \n");
		System.out.print("            2. Non-Vegetarian Food.\n");
		System.out.print("            3. Chineese Food.         \n");
		System.out.print("            4. Exit                        \n");
		System.out.print("Enter your choice: ");
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); 
		choice=Integer.parseInt(br.readLine());
		switch (choice) {
		case 1:{ 
		    	 VegFood vf=new VegFood();
			  System.out.println(vf.prepareFood());
			  System.out.println( vf.foodPrice());
			}
			break;
			
                case 2:{
		        Food f1=new NonVegFood((Food) new VegFood());
	                System.out.println(f1.prepareFood());
		        System.out.println( f1.foodPrice());
		}
			break;	
     case 3:{
		     Food f2=new ChineeseFood((Food) new VegFood());
                     System.out.println(f2.prepareFood());
                    System.out.println( f2.foodPrice());
              }
			break;	
			
         default:{  
			System.out.println("Other than these no food available");
		}		
	return;
     }//end of switch
		
}while(choice!=4);
	}
}

输出量

========= Food Menu ============
            1. Vegetarian Food.
            2. Non-Vegetarian Food.
            3. Chineese Food.
            4. Exit
Enter your choice: 1
Veg Food
50.0
========= Food Menu ============
            1. Vegetarian Food.
            2. Non-Vegetarian Food.
            3. Chineese Food.
            4. Exit
Enter your choice: 2
Veg Food With Roasted Chiken and Chiken Curry
200.0
========= Food Menu ============
            1. Vegetarian Food.
            2. Non-Vegetarian Food.
            3. Chineese Food.
            4. Exit
Enter your choice: 3
Veg Food With Fried Rice and Manchurian
115.0
========= Food Menu ============
            1. Vegetarian Food.
            2. Non-Vegetarian Food.
            3. Chineese Food.
            4. Exit
Enter your choice: 4
Other than these no food available