普通开发模式下的代码是编译时已经设置好参数和属性， 反射是在运行时候动态注入参数属性

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Class 类

  • 在jvm 中代表 类和接口 的类
  • Class 对象具体包含了某个特定类的结构信息
  • 通过Class 对象可以获取到类的构造方法、方法、成员变量等

  • image.png ```java public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {

    1.   //ClassNotFoundException  类找不到
    2.   //InstantiationException   非法访问异常
    3.   //IllegalAccessException  无法实例化异常
    5.   // 指定的类加载到jvm中，  返回对应的class 对象
    6.   Class employeeClass = Class.forName("cn.ichief.reflect.entity.Employee");
    8.   // 通过默认构造方法实例对象   默认使用无参数的    newInstance    返回的是Object  需要强制转换
    9.   Employee employee = (Employee) employeeClass.newInstance();
  1. }
  1. <a name="FANjH"></a>
  2. #### Constructor 构造方法类
  4. - ![image.png](https://cdn.nlark.com/yuque/0/2021/png/422907/1639283946710-6b7303a0-b444-45cf-b09b-a70afd8652e9.png#clientId=ud9167f32-073b-4&from=paste&height=316&id=uec2d8a47&margin=%5Bobject%20Object%5D&name=image.png&originHeight=632&originWidth=2586&originalType=binary&ratio=1&size=591295&status=done&style=none&taskId=u3735c32c-26e6-4b29-8204-f496dd79d52&width=1293)
  5. ```java
  6.  try {
  7.             Class EmployeeClass = Class.forName("cn.ichief.reflect.entity.Employee");
  9.             // 对应构造方法的参数类型
  10.             Constructor constructor = EmployeeClass.getConstructor(new Class[]{
  11.                     Integer.class,
  12.                     String.class,
  13.                     Float.class,
  14.                     String.class
  15.             });
  17.             Employee employee = (Employee) constructor.newInstance(new Object[]{
  18.                     100, "ss", 3000f, "yfb"
  19.             });
  22.         } catch (ClassNotFoundException e) {
  23.             e.printStackTrace();
  24.         } catch (NoSuchMethodException e) {
  25.             e.printStackTrace();
  26.         } catch (InvocationTargetException e) {
  27.             e.printStackTrace();
  28.         } catch (InstantiationException e) {
  29.             e.printStackTrace();
  30.         } catch (IllegalAccessException e) {
  31.             e.printStackTrace();
  32.         }

Method 方法类

  • image.png ```java public static void main(String[] args) {

    1.   try {
    2.       Class EmployeeClass = Class.forName("cn.ichief.reflect.entity.Employee");
    4.       // 对应构造方法的参数类型
    5.       Constructor constructor = EmployeeClass.getConstructor(new Class[]{
    6.               Integer.class,
    7.               String.class,
    8.               Float.class,
    9.               String.class
    10.       });
    12.       Employee employee = (Employee) constructor.newInstance(new Object[]{
    13.               100, "ss", 3000f, "yfb"
    14.       });
  1.         Method updateSalaryMethod = EmployeeClass.getMethod("updateSalary", Float.class);
  3.         Employee employee1 = (Employee) updateSalaryMethod.invoke(employee, 100f);
  5.     } catch (ClassNotFoundException e) {
  6.         e.printStackTrace();
  7.     } catch (NoSuchMethodException e) {
  8.         e.printStackTrace();
  9.     } catch (InvocationTargetException e) {
  10.         e.printStackTrace();
  11.     } catch (InstantiationException e) {
  12.         e.printStackTrace();
  13.     } catch (IllegalAccessException e) {
  14.         e.printStackTrace();
  15.     }
  16. }
  1. <a name="l2DTV"></a>
  2. #### Field 成员变量类
  4. - ![image.png](https://cdn.nlark.com/yuque/0/2021/png/422907/1639284803877-2be23cc2-f17a-4adb-b53c-aa8c6594c297.png#clientId=ud9167f32-073b-4&from=paste&height=642&id=ud0380cd4&margin=%5Bobject%20Object%5D&name=image.png&originHeight=1284&originWidth=2416&originalType=binary&ratio=1&size=634266&status=done&style=none&taskId=ua885e5b5-83ee-4ff2-9fa4-f5eb5da12c5&width=1208)
  5. - ![image.png](https://cdn.nlark.com/yuque/0/2021/png/422907/1639284816663-be036d98-94f4-4d60-ad1c-1171e6979390.png#clientId=ud9167f32-073b-4&from=paste&height=437&id=u6cceaaad&margin=%5Bobject%20Object%5D&name=image.png&originHeight=874&originWidth=2702&originalType=binary&ratio=1&size=735030&status=done&style=none&taskId=u0c1031ca-b2c8-4696-a26c-8086e507cc8&width=1351)
  6. ```java
  7. public static void main(String[] args) {
  8.         try {
  9.             Class EmployeeClass = Class.forName("cn.ichief.reflect.entity.Employee");
  11.             // 对应构造方法的参数类型
  12.             Constructor constructor = EmployeeClass.getConstructor(new Class[]{
  13.                     Integer.class,
  14.                     String.class,
  15.                     Float.class,
  16.                     String.class
  17.             });
  19.             Employee employee = (Employee) constructor.newInstance(new Object[]{
  20.                     100, "ss", 3000f, "yfb"
  21.             });
  23.             Field enameField = EmployeeClass.getField("ename");
  25.             enameField.set(employee, "ssssd");
  27.             String ename = enameField.get(employee).toString();
  30.         } catch (ClassNotFoundException e) {
  31.             e.printStackTrace();
  32.         } catch (NoSuchMethodException e) {
  33.             e.printStackTrace();
  34.         } catch (InvocationTargetException e) {
  35.             e.printStackTrace();
  36.         } catch (InstantiationException e) {
  37.             e.printStackTrace();
  38.         } catch (IllegalAccessException e) {
  39.             e.printStackTrace();
  40.         } catch (NoSuchFieldException e) {
  41.             e.printStackTrace();
  42.         }
  43.     }

getConstructor 只能获取public private 的使用 getDeclaredConstructor

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