先通过例子理解一下

第1步：创建一个接口

Shape.java

1 public interface Shape {2    void draw();3 }

第2步：创建几个实现类

Rectangle.java

1 public class Rectangle implements Shape {2 3    @Override4    public void draw() {5       System.out.println("Inside Rectangle::draw() method.");6    }7 }

Square.java

1 public class Square implements Shape {2 3    @Override4    public void draw() {5       System.out.println("Inside Square::draw() method.");6    }7 }

Circle.java

1 public class Circle implements Shape {2 3    @Override4    public void draw() {5       System.out.println("Inside Circle::draw() method.");6    }7 }

第3步：创建工厂根据给定的信息生成具体类的对象

ShapeFactory.java

1 public class ShapeFactory { 2  3    //use getShape method to get object of type shape  4    public Shape getShape(String shapeType){ 5       if(shapeType == null){ 6          return null; 7       }         8       if(shapeType.equalsIgnoreCase("CIRCLE")){ 9          return new Circle();10 11       } else if(shapeType.equalsIgnoreCase("RECTANGLE")){12          return new Rectangle();13 14       } else if(shapeType.equalsIgnoreCase("SQUARE")){15          return new Square();16       }17 18       return null;19    }20 }

第4步：演示使用工厂通过传递类型等信息来获取具体类的对象

FactoryPatternDemo.java

1 public class FactoryPatternDemo { 2  3    public static void main(String[] args) { 4       ShapeFactory shapeFactory = new ShapeFactory(); 5  6       //get an object of Circle and call its draw method. 7       Shape shape1 = shapeFactory.getShape("CIRCLE"); 8  9       //call draw method of Circle10       shape1.draw();11 12       //get an object of Rectangle and call its draw method.13       Shape shape2 = shapeFactory.getShape("RECTANGLE");14 15       //call draw method of Rectangle16       shape2.draw();17 18       //get an object of Square and call its draw method.19       Shape shape3 = shapeFactory.getShape("SQUARE");20 21       //call draw method of circle22       shape3.draw();23    }24 }

第5步：验证输出结果

验证输出结果如下：

1 Inside Circle::draw() method.2 Inside Rectangle::draw() method.3 Inside Square::draw() method.