Design Pattern 简明教程

Design Pattern - Factory Pattern

工厂模式是 Java 中使用最广泛的设计模式之一。这种设计模式属于创建模式，因为该模式提供了创建对象的最佳方法之一。

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

Implementation

我们将创建 Shape 接口和实现 Shape 接口的具体类。作为下一步，将工厂类 ShapeFactory 定义为。

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

Step 1

创建一个接口。

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

创建工厂来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;
   }
}

Step 4

使用工厂获取具体类的对象，方法是传递类型等信息。

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.