4、反射-类的构造器：Constrctor

类的构造器：Constrctor

        Class clazz = Class.forName("cn.com.mrchengs.constrctor.Student");

        //1、获取全部的构造器
        Constructor[] constructors = clazz.getConstructors();
        for (Constructor constructor : constructors){
            System.out.println(constructor);
        }

        //2、获取某一个构造器
        Constructor<Student> constructor = clazz.getConstructor(String.class, int.class);
        System.out.println(constructor);

        //3、调用newInstance()方法创建对象
        Student student = constructor.newInstance("MrChengs", 22);
        System.out.println(student);

小实例

//要求Student中的age的范围再0-100
    //通过反射的方式感知到方法
    @Test
    public void  test() throws ClassNotFoundException, NoSuchMethodException, 
　　　　　　　　IllegalAccessException, InvocationTargetException, InstantiationException {

        Class clazz = Class.forName("cn.com.mrchengs.constrctor.Student");

        Object obj = clazz.newInstance();
        
        Method method = clazz.getDeclaredMethod("setAge", int.class);
        method.setAccessible(true);
        
        int val = 20;
        
        Annotation an = method.getAnnotation(AgeValidator.class);
        if(an != null){
            if(val < 0 || val > 100){
                throw new RuntimeException("非法的年龄");
            }
        }
        
        method.invoke(obj, 10);
        System.out.println(obj);
    } 

 自定义注解

@Retention(RetentionPolicy.RUNTIME)//运行时可见
@Target(value={ElementType.METHOD})
public @interface AgeValidator {

}

 Student

    @AgeValidator
    public void setAge(int age) {
        this.age = age;
    }