4.Class.forName()示例

需求

有如下动物类和动物工厂类，分别创建动物类对象。
动物类

//动物
interface Animal {
    public void eat();
}
class Cat implements Animal {
    @Override
    public void eat() {
        System.out.println("猫吃鱼");
    }
}
class Dog implements Animal {
    @Override
    public void eat() {
        System.out.println("狗吃肉");
    }
}
class Monkey implements Animal {
    @Override
    public void eat() {
        System.out.println("猴子吃香蕉");
    }
}

工厂类

interface Factory {
    public Animal createAnimal();
}
class CatFactory  implements Factory{
    @Override
    public Animal createAnimal() {
        return new Cat();
    }
}
class DogFactory implements Factory {
    @Override
    public Animal createAnimal() {
        return new Dog();
    }
}
class MonkeyFactory implements Factory {
    @Override
    public Animal createAnimal() {
        return new Monkey();
    }
}

未使用反射时

    @Test
    public void demo1(){
        Factory factory = new DogFactory();    //创建榨汁机
        Animal animal = factory.createAnimal();
        animal.eat();//狗吃肉
        factory = new CatFactory();//创建榨汁机
        animal = factory.createAnimal();
        animal.eat();//猫吃鱼
    }

使用Class.forName API 创建实例

@Test
public void demo2() throws ClassNotFoundException, InstantiationException, IllegalAccessException {
    Class clazz = Class.forName("cn.giteasy.reflect.DogFactory");
    Factory factory = (Factory) clazz.newInstance();
    Animal animal = factory.createAnimal();
    animal.eat();
}

读取配置文件创建类的实例

cn.giteasy.reflect.MonkeyFactory
cn.giteasy.reflect.CatFactory
cn.giteasy.reflect.DogFactory

    @Test
    public void demo3() throws ClassNotFoundException, InstantiationException, IllegalAccessException, IOException {
        //需要修改要创建的类时，只需要修改配置文件即可
        BufferedReader br = new BufferedReader(new FileReader("config.properties"));
        Class clazz;
        Factory factory;
        List<String> list = br.lines().collect(Collectors.toList());
        for (String line : list) {
            clazz = Class.forName(line); //获取该类的字节码文件
            factory = (Factory) clazz.newInstance();//创建实例对象
            Animal animal = factory.createAnimal();
            animal.eat();
        }

        /**
         * 输出结果：
         *
         * 猴子吃香蕉
         * 猫吃鱼
         * 狗吃肉
         */
    }