简单工厂模式

作用

• 为类的创建提供统一的接口

public class ShapeFactory {

    public static Shape getShape(String className) {

        ClassLoader classLoader = ShapeFactory.class.getClassLoader();
        try {
            Class<Shape> aClass = (Class<Shape>) classLoader.loadClass(className);
            // 实例 instanceof (类);
            //自身类.class.isInstance(自身实例或子类实例)  类和实例比对
            boolean flag = Shape.class.isAssignableFrom(aClass); //前面时父类，后面时子类 类和类比对
            if (flag) {
                Shape shape = aClass.newInstance();
                return shape;
            }

        } catch (ClassNotFoundException e) {
            throw new RuntimeException("类名错了");
        } catch (InstantiationException e) {
           throw new RuntimeException("没有无参构造器");
        } catch (IllegalAccessException e) {
           throw new RuntimeException("修饰符错误");
        }

       throw new RuntimeException("不是shape类");
    }

}