Java工厂设计模式课程详解

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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。

在工厂模式中，我们没有创建逻辑暴露给客户端创建对象，并使用一个通用的接口引用新创建的对象。 （推荐学习：java课程）

实现方法

我们将创建一个Shape接口和实现Shape接口的具体类。一个工厂类ShapeFactory会在下一步中定义。

FactoryPatternDemo这是一个演示类，将使用ShapeFactory来获取一个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。

实现工厂模式的结构如下图所示 -

第1步

创建一个接口-

复制代码Shape.java
public interface Shape {
   void draw();
}1
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Shape.java
public interface Shape {
   void draw();
}
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第2步

创建实现相同接口的具体类。如下所示几个类 -

复制代码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.");
   }
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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.");
   }
}
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第3步

创建工厂根据给定的信息生成具体类的对象。

复制代码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;
   }
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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;
   }
}
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第4步

使用工厂通过传递类型等信息来获取具体类的对象。

复制代码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 circle
      shape3.draw();
   }
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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 circle
      shape3.draw();
   }
}
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第5步

验证输出结果如下-

复制代码Inside Circle::draw() method.
Inside Rectangle::draw() method.
Inside Square::draw() method.1
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Inside Circle::draw() method.
Inside Rectangle::draw() method.
Inside Square::draw() method.
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