反射学习的记录

### 问题1 怎样通过类名获取反射对象？
```java
        String name = Person.class.getName();
        //获取类对象
        Class<?> clazz = Class.forName(name);
        //示例化对象
        Object o = clazz.newInstance();
```
### 问题2 怎样给反射对象赋值？
```java
   String name = Person.class.getName();
        //获取类对象
        Class<?> clazz = Class.forName(name);
        //示例化对象
        Object o = clazz.newInstance();
        Field field = o.getClass().getDeclaredField("age");
        field.setAccessible(true);
        //反射赋值
        field.set(o,2);
```
### 问题3 怎样调用反射方法？
```java
{
        String name = Person.class.getName();
        //获取类对象
        Class<?> clazz = Class.forName(name);
        //示例化对象
        Object o = clazz.newInstance();
        Field field = o.getClass().getDeclaredField("age");
        Field fieldName = o.getClass().getDeclaredField("name");
        field.setAccessible(true);
        //反射赋值
        field.set(o,2);
        fieldName.set(o,"小王");
        System.out.println(o.toString());
        //反射调用指定方法
        Method[] methods = clazz.getMethods();
        //也可以获取到方法
        Method methodSetName = clazz.getMethod("setName",String.class);
        methodSetName.invoke(o,"小王真帅");
        for(Method method: methods)
        {
            String methodName = method.getName();
            //方法名称
            if("getName".equals(methodName))
            {
                //调用方法 对象，传参
                Object invoke = method.invoke(o, null);
            }
        }
        
        

    }
```
### 问题4 反射获取注解内容
```java
//获取自定义注解 @Server 该类的所有注解
        System.out.println("--------class----------");
        if (clazz.isAnnotationPresent(Server.class))
        {
            Server annotation = clazz.getAnnotation(Server.class);
            String value = annotation.value();
            System.out.println(value);
        }
        //通过反射获取@Server注解的值
        Annotation[] annotations = clazz.getAnnotations();
        //获取到所有的注解
        for (Annotation ans : annotations)
        {
            Class<? extends Annotation> server = ans.getClass();
            Field[] fields = server.getFields();
            Method[] fms = server.getMethods();
            for (Method fm : fms)
            {
                if ("value".equals(fm.getName()))
                {
                    Object invoke = fm.invoke(ans, null);
                    System.out.println(invoke);
                }
            }
        }
        System.out.println("--------Field----------");
        // 获取自定义@UserName @UserAge 定义在属性内
        Field[] declaredFields = clazz.getDeclaredFields();
        for (Field dfs : declaredFields)
        {
            if (dfs.isAnnotationPresent(UserName.class))
            {
                UserName annotation = dfs.getAnnotation(UserName.class);
                String name1 = annotation.name();
                System.out.println("@UserName " + name1);
            }
            if (dfs.isAnnotationPresent(UserAge.class))
            {
                UserAge annotation = dfs.getAnnotation(UserAge.class);
                int age = annotation.age();
                System.out.println("@UserAge " + age);
            }
        }
        System.out.println("--------Method----------");
        Method[] declaredMethods = clazz.getDeclaredMethods();
        for (Method ds : declaredMethods)
        {
            if (ds.isAnnotationPresent(UserMethod.class))
            {
                UserMethod annotation = ds.getAnnotation(UserMethod.class);
                String value = annotation.value();
                System.out.println("@Method "+ value);
            }
        }
```

### 5.反射获取注解内容然后赋值给
```java
 //获取到注解赋值
        System.out.println("-------注解赋值------");
        Field[] declareds = clazz.getDeclaredFields();
        for (Field dfs : declareds)
        {
            if (dfs.isAnnotationPresent(UserName.class))
            {
                UserName annotation = dfs.getAnnotation(UserName.class);
                String name1 = annotation.name();
                System.out.println("@UserName " + name1);
                dfs.setAccessible(true);
                dfs.set(o,name1);
            }
            if (dfs.isAnnotationPresent(UserAge.class))
            {
                UserAge annotation = dfs.getAnnotation(UserAge.class);
                int age = annotation.age();
                System.out.println("@UserAge " + age);
                dfs.setAccessible(true);
                dfs.set(o,age);
            }
        }
        System.out.println(o.toString());
```