工厂模式（ Factory Pattern）

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2023-12-01

工厂模式是Java中最常用的设计模式之一。这种类型的设计模式属于创建模式，因为此模式提供了创建对象的最佳方法之一。

在Factory模式中，我们创建对象而不将创建逻辑暴露给客户端，并使用公共接口引用新创建的对象。

实现 (Implementation)

我们将创建一个Shape接口和实现Shape接口的具体类。工厂类ShapeFactory被定义为下一步。

FactoryPatternDemo ，我们的演示类将使用ShapeFactory来获取Shape对象。它会将信息（ CIRCLE/RECTANGLE/SQUARE ）传递给ShapeFactory以获取所需的对象类型。

Step 1

创建一个界面。

Shape.java

public interface Shape {
   void draw();
}

Step 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.");
   }
}

Step 3

创建工厂以根据给定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;
   }
}

Step 4

使用Factory通过传递类型等信息来获取具体类的对象。

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();
   }
}

Step 5

验证输出。

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