工厂模式：
工厂模式通过工厂创建对象，用户无需注意内部细节，只需要调用工厂类，
将需要创建的类名称传递给工厂即可。
采用工程类创建，最后返回的是接口类型，所以只用关心接口，不用关心接口的具体实现类。
Shape接口
public interface Shape { public void draw(); }
实现Shape接口的具体类：
public class Circle implements Shape{ @Override public void draw() { System.out.println("draw circle"); } }
public class Rectangle implements Shape{ @Override public void draw() { System.out.println("draw rectangle"); } }
public class Square implements Shape{ @Override public void draw() { System.out.println("draw square"); } }
ShapeFactory工厂：
public class ShapeFactory { public Shape getShape(String shape) {//传递图像字符串，根据字符串判断并实例化对应对象 if("circle".equals(shape)) { return new Circle(); }else if("rectangle".equals(shape)) { return new Rectangle(); }else if("square".equals(shape)) { return new Square(); } return null; } }
Main调用ShapeFactory实例化对象
public class Main { public static void main(String[] args) { ShapeFactory shapeFactory = new ShapeFactory(); Shape circle = shapeFactory.getShape("circle"); circle.draw(); } }
运行结果：
draw circle
ShapeFatory中采用if else，当工厂中类多了后采用if else不易于扩展，且代码结构复杂不好分析。
故将图形用枚举类型代替，结合switch代替if else.
图形枚举
public enum ShapeEnum { CIRCLE,RECTANGLE,SQUARE }
ShapeFactory
public class ShapeFactory { public Shape getShape(ShapeEnum shape) { switch(shape) { case CIRCLE: return new Circle(); case RECTANGLE: return new Rectangle(); case SQUARE: return new Square(); default : try {//没有找到指定类型则抛出ClassNotFound异常 throw new ClassNotFoundException(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } } return null; } }
Main
public class Main { public static void main(String[] args) { ShapeFactory shapeFactory = new ShapeFactory(); Shape circle = shapeFactory.getShape(ShapeEnum.CIRCLE); circle.draw(); } }
运行结果：
draw circle
参考资料：
http://www.runoob.com/design-pattern/factory-pattern.html
原文：https://www.cnblogs.com/huang-changfan/p/10692258.html