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