Java的工厂模式简介

在下面的章节中，我们将展示如何使用工厂模式来创建对象。

由工厂模式创建的对象将是形状的物体，如圆形，矩形。

首先，我们设计代表形状的接口。

public interface Shape {
   void draw();
}

然后，我们创建具体的类实现该接口。

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.\");
   }
}

核心工厂模式是工厂类。下面的代码演示如何创建一个工厂类Shape对象。

该ShapeFactory类创建基于传递到getShape（）方法的字符串值Shape对象。如果字符串值是圆，它会创建一个Circle对象。

public class ShapeFactory {
  
   //use getShape method to get   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;
   }
}

下面的代码有mian方法，它采用工厂类传递一个信息，如类型，以获得具体类的对象。

public class Main {

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

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

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

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

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

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

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