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。

Factory pattern is one of the most used design patterns in Java. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object.

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。

In Factory pattern, we create object without exposing the creation logic to the client and refer to newly created object using a common interface.

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。

We’re going to create a Shape interface and concrete classes implementing the Shape interface. A factory class ShapeFactory is defined as a next step.

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。

FactoryPatternDemo, our demo class will use ShapeFactory to get a Shape object. It will pass information (CIRCLE / RECTANGLE / SQUARE) to ShapeFactory to get the type of object it needs.

Step 1

创建一个接口。

Create an interface.

Shape.java

public interface Shape {
   void draw();
}

Step 2

创建实现相同接口的具体类。

Create concrete classes implementing the same interface.

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。

Create a Factory to generate object of concrete class based on given information.

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。

Use the Factory to get object of concrete class by passing an information such as type.

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。

Verify the output.

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