设计模式 - 工厂模式



工厂模式是Java中最常用的设计模式之一。这种设计模式属于创建型模式,因为它提供了一种创建对象的好方法。

在工厂模式中,我们创建对象而不向客户端公开创建逻辑,并使用公共接口引用新创建的对象。

实现

我们将创建一个Shape接口和实现Shape接口的具体类。下一步定义一个工厂类ShapeFactory

我们的演示类FactoryPatternDemo将使用ShapeFactory来获取Shape对象。它将信息(CIRCLE / RECTANGLE / SQUARE)传递给ShapeFactory以获取它需要的对象类型。

Factory Pattern UML Diagram

步骤1

创建一个接口。

Shape.java

public interface Shape {
   void draw();
}

步骤2

创建实现相同接口的具体类。

Rectangle.java

public class Rectangle implements Shape {

   @Override
   public void draw() {
      System.out.println("Inside Rectangle::draw() method.");
   }
}

Square.java

public class Square implements Shape {

   @Override
   public void draw() {
      System.out.println("Inside Square::draw() method.");
   }
}

Circle.java

public class Circle implements Shape {

   @Override
   public void draw() {
      System.out.println("Inside Circle::draw() method.");
   }
}

步骤3

创建一个工厂,根据给定的信息生成具体类的对象。

ShapeFactory.java

public class ShapeFactory {
	
   //use getShape method to get object of type shape 
   public Shape getShape(String shapeType){
      if(shapeType == null){
         return null;
      }		
      if(shapeType.equalsIgnoreCase("CIRCLE")){
         return new Circle();
         
      } else if(shapeType.equalsIgnoreCase("RECTANGLE")){
         return new Rectangle();
         
      } else if(shapeType.equalsIgnoreCase("SQUARE")){
         return new Square();
      }
      
      return null;
   }
}

步骤4

通过传递诸如类型之类的信息,使用工厂获取具体类的对象。

FactoryPatternDemo.java

public class FactoryPatternDemo {

   public static void main(String[] args) {
      ShapeFactory shapeFactory = new ShapeFactory();

      //get an object of Circle and call its draw method.
      Shape shape1 = shapeFactory.getShape("CIRCLE");

      //call draw method of Circle
      shape1.draw();

      //get an object of Rectangle and call its draw method.
      Shape shape2 = shapeFactory.getShape("RECTANGLE");

      //call draw method of Rectangle
      shape2.draw();

      //get an object of Square and call its draw method.
      Shape shape3 = shapeFactory.getShape("SQUARE");

      //call draw method of square
      shape3.draw();
   }
}

步骤5

验证输出。

Inside Circle::draw() method.
Inside Rectangle::draw() method.
Inside Square::draw() method.
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