工廠模式是Java中最常用的設計模式之一。這種型別的設計模式屬於建立模式，因為此模式提供了建立物件的最佳方法之一。

在Factory模式中，我們建立物件而不將建立邏輯暴露給客戶端，並使用公共介面引用新建立的物件。

履行

我們將建立一個Shape介面和實現Shape介面的具體類。工廠類ShapeFactory被定義為下一步。

FactoryPatternDemo，我們的演示類將使用ShapeFactory來獲取Shape物件。它會將資訊（CIRCLE / RECTANGLE / SQUARE）傳遞給ShapeFactory以獲取所需的物件型別。

步驟1

建立一個介面。

Shape.java

public interface Shape {
   void draw();
}

第2步

建立實現相同介面的具體類。

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.");
   }
}

第3步

建立工廠以根據給定資訊生成具體類的物件。

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;
   }
}

步驟4

使用Factory通過傳遞型別等資訊來獲取具體類的物件。

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();
   }
}

第5步

驗證輸出。

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