在工厂模式里,我们不用向客户端暴露创建逻辑而能创建对象。
例子
下面展示如何使用工厂模式去创建对象。
该工厂模式将创建形状的对象,比如圆、长方形。
首先我们设计一个表示形状(Shape)的接口。
public interface Shape { void draw(); }
接着我们创建具体类实现该接口。
以下是Rectangle.java的代码
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."); } }
工厂模式的核心是工厂类。以下代码展示如何给Shape对象创建工厂类。
ShapeFactory类基于传入getShape()方法的字符串类型而创建Shape对象。如果字符串值是CIRCLE,它就创建一个Circle对象。
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; } }
以下代码包含main方法,而它通过传递形状的type信息而使用工厂类去取得具体类的对象。
public class Main { 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(); } }
以上代码生成以下结果。
Inside Circle::draw() method. Inside Rectangle::draw() metod. Inside Square::draw() metod.