目录
一、注解
1、注解入门
//什么是注解
public class Demo01_Annotation extends Object {
//@Override就是一个注解
@Override
public String toString() {
return super.toString();
}
}
2、内置注解
// 什么是注解
public class Demo01_Annotation extends Object {
// @Override就是一个注解
@Override
public String toString() {
return super.toString();
}
// @Deprecated不推荐程序员使用,但是可以使用,或者存在更好的更新方式
@Deprecated
public static void test() {
System.out.println("Deprecated");
}
// @SuppressWarnings 镇压警告
@SuppressWarnings("all")
public void test01(){
List<String> list = new ArrayList<String>();
}
public static void main(String[] args) {
test();
}
}
3、自定义注解,元注解
//测试元注解
@MyAnnotation
public class Demo02_MetaAnnotation {
@MyAnnotation
public void test() {
}
}
//定义一个注解
//@Target可以用在什么地方
//ElementType.METHOD方法上有效 ElementType.TYPE类上有效
@Target(value = {
ElementType.METHOD, ElementType.TYPE})
//@Retention在什么地方有效
//RUNTIME>CLASS>SOURCES
@Retention(value = RetentionPolicy.RUNTIME)
//@Documented 表示是否将我们的注解生成在Javadoc中
@Documented
//@Inherited 子类可以继承父类的注解
@Inherited
@interface MyAnnotation {
}
//自定义注解
public class Demo03_CustomAnnotation {
//注解可以显示赋值,如果没有默认值,就必须给注解赋值
@MyAnnotation2(name = "张三")
public void test() {
}
}
@Target(value = {
ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnotation2 {
//注解的参数:参数类型+参数名()
//String name();
String name() default "";
int age() default 0;
int id() default -1;//-1代表不存在
String[] schools() default {
"西部开源","清华大学"};
二、反射机制
1、Java反射机制概念
1.1 静态 & 动态语言
1.2 反射机制概念
1.3 反射机制研究与应用
1.4 反射机制优缺点
1.5 实现
package com.bobo.util.reflection.src.com.mao.reflection;
//什么叫反射
public class Test02 {
public static void main(String[] args) throws ClassNotFoundException {
// 通过反射获取类的class对象
Class<?> c = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.User");
System.out.println(c);
Class<?> c1 = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.User");
Class<?> c2 = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.User");
Class<?> c3 = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.User");
Class<?> c4 = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.User");
// 一个类在内存中只有一个Class对象
// 一个类被加载后,类的整个结构都会被封装在Class对象中
/**
* public native int hashCode();返回该对象的hash码值
* 注:哈希值是根据哈希算法算出来的一个值,这个值跟地址值有关,但不是实际地址值。
*/
System.out.println(c1.hashCode());
System.out.println(c2.hashCode());
System.out.println(c3.hashCode());
System.out.println(c4.hashCode());
/**
* 460141958
* 460141958
* 460141958
* 460141958
* */
}
}
//实体类
class User {
private String name;
private int id;
private int age;
public User() {
// 无构造器
}
public User(String name, int id, int age) {
this.name = name;
this.id = id;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getId() {
return id;
}
public void setId( int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
", id=" + id +
", age=" + age +
'}';
}
}
2、理解Class类并获取Class实例
2.1 class类介绍
2.2 获取Class类的实例
package com.bobo.util.reflection.src.com.mao.reflection;
//测试class类的创建方式有哪些
public class Test03 {
public static void main(String[] args) throws ClassNotFoundException {
Person person = new student();
System.out.println("这个人是:"+person.hashCode());
//方式1:通过对象获得 1163157884
Class aClass1 = person.getClass();
System.out.println(aClass1.hashCode());
//方式2:forname获取 1163157884
Class aClass2 = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.student");
System.out.println(aClass2.hashCode());
//方式3:通过类名.class 获得 1163157884
Class studentClass = student.class;
System.out.println(studentClass.hashCode());
//方式4:基本内置类型的包装类都有一个Type 属性
final Class type = Integer.TYPE;
System.out.println(type); // int
//方式5:获得父类类型
final Class superclass = aClass1.getSuperclass();
System.out.println(superclass);
// class com.bobo.util.reflection.src.com.mao.reflection.Test03$Person
}
static class Person{
public String name;
public Person() {
}
public Person(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
'}';
}
}
}
class student extends Test03.Person {
public static int a = 3;
public static int getA() {
return a;
}
public static void setA(int a) {
student.a = a;
}
public student() {
this.name="学生";
}
}
class teacher extends Test03.Person {
public teacher() {
this.name="老师";
}
}
2.3 哪些类型可以有Class对象
package com.bobo.util.reflection.src.com.mao.reflection;
import java.lang.annotation.ElementType;
// 所有类型的class
public class Test04 {
public static void main(String[] args) {
//类
Class c1 = Object.class; // class java.lang.Object
//接口
Class c2 = Comparable.class; // interface java.lang.Comparable
//一维数组
Class c3 = String[].class; // class [Ljava.lang.String;
//二维数组
Class c4 = int[][].class; // class [[I
//注解
Class c5 = Override.class; // interface java.lang.Override
//枚举
Class c6 = ElementType.class; // class java.lang.annotation.ElementType
//基本类型
Class c7 = Integer.class; // class java.lang.Integer
//void
Class c8 = void.class; // void
// Class
Class c9 = Class.class; // class java.lang.Class
System.out.println(c1);
System.out.println(c2);
System.out.println(c3);
System.out.println(c4);
System.out.println(c5);
System.out.println(c6);
System.out.println(c7);
System.out.println(c8);
System.out.println(c9);
//只要元素类型与维度一样,就是同Class
int[] a = new int[10];
int[] b = new int[100];
System.out.println(a.getClass().hashCode()); // 460141958
System.out.println(b.getClass().hashCode()); // 460141958
}
}
3、类的加载与ClassLoader
3.1 Java内存分析
3.2 类的加载
package com.bobo.util.reflection.src.com.mao.reflection;
//类加载
public class Test05 {
public static void main(String[] args) {
final A a = new A();
System.out.println(A.m);
/**
* A类静态代码块初始化
* A类的无参构造初始化
* 100
* */
/*
* 1、加载到内存,会产生一个类对应class对象
* 2、链接,链接结束后 m=0
* 3、初始化
* <clinit>(){
* System.out.println("A类静态代码块初始化");
m =300;
* m=100;
* }
* m=100;
* */
}
}
class A{
static {
System.out.println("A类静态代码块初始化");
int m =300;
}
static int m=100;
public A() {
System.out.println("A类的无参构造初始化");
}
}
分析上面代码
程序自上往下执行
3.3 什么时候会发生类初始化
package com.bobo.util.reflection.src.com.mao.reflection;
public class Test06 {
static {
System.out.println("Main类被加载");
}
public static void main(String[] args) throws ClassNotFoundException {
// 1. 主动调用
// Son son = new Son();
/**
* Main类被加载
* 父类被加载
* 子类被加载
* */
// 反射也会产生主动引用
// Class.forName("com.bobo.util.reflection.src.com.mao.reflection.Son");
/**
* Main类被加载
* 父类被加载
* 子类被加载
* */
//不会产生类的引用的方法
// System.out.println(Son.b);
/**
* Main类被加载
* 父类被加载
* 2
* */
//Son[] array = new Son[5];
System.out.println(Son.M);
/**
* Main类被加载
* 1
* */
}
}
class Father {
static int b = 2;
static {
System.out.println("父类被加载");
}
}
class Son extends Father {
static {
System.out.println("子类被加载");
m = 100;
}
static int m = 300;
static final int M = 1;
}
3.4 类加载器的作用
ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();//获取系统类的加载器
ClassLoader parent = systemClassLoader.getParent();//获取系统类加载器的父类加载器–>扩展类加载器 jre1.8.0_91\lib\ext
ClassLoader parent1 = parent.getParent();//获取扩展类加载器父类加载器–>根加载器(c/c++) jre1.8.0_91\lib\rt.jar
package com.bobo.util.reflection.src.com.mao.reflection;
// 类加载器
public class Test07 {
public static void main(String[] args) throws ClassNotFoundException {
//获取系统类的加载器
ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
System.out.println(systemClassLoader); //sun.misc.Launcher$AppClassLoader@18b4aac2
//获取系统类加载器的父类加载器-->扩展类加载器 jre1.8.0_91\lib\ext
ClassLoader parent = systemClassLoader.getParent();
System.out.println(parent); // sun.misc.Launcher$ExtClassLoader@1b6d3586
//获取扩展类加载器父类加载器-->根加载器(c/c++) jre1.8.0_91\lib\rt.jar
ClassLoader parent1 = parent.getParent();
System.out.println(parent1); // null
//测试当前类是哪个加载器加载的
ClassLoader classLoader = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.Test07").getClassLoader();
System.out.println(classLoader); // sun.misc.Launcher$AppClassLoader@18b4aac2
//测试JDK内置的类是谁加载的
classLoader = Class.forName("java.lang.Object").getClassLoader();
System.out.println(classLoader); //null
//如何获得系统类加载器可以加载的路径
System.out.println(System.getProperty("java.class.path"));
//双亲委派机制 检测安全性 你写的类和跟加载器一样的不会用你写的类
//java.lang.String -->往上推
/*
* E:\Program Files\Java\jre\lib\charsets.jar;
* E:\Program Files\Java\jre\lib\deploy.jar;
* E:\Program Files\Java\jre\lib\ext\access-bridge-64.jar;
* E:\Program Files\Java\jre\lib\ext\cldrdata.jar;
* E:\Program Files\Java\jre\lib\ext\dnsns.jar;
* E:\Program Files\Java\jre\lib\ext\jaccess.jar;
* E:\Program Files\Java\jre\lib\ext\jfxrt.jar;
* E:\Program Files\Java\jre\lib\ext\localedata.jar;
* E:\Program Files\Java\jre\lib\ext\nashorn.jar;
* E:\Program Files\Java\jre\lib\ext\sunec.jar;
* E:\Program Files\Java\jre\lib\ext\sunjce_provider.jar;
* E:\Program Files\Java\jre\lib\ext\sunmscapi.jar;
* E:\Program Files\Java\jre\lib\ext\sunpkcs11.jar;
* E:\Program Files\Java\jre\lib\ext\zipfs.jar;
* E:\Program Files\Java\jre\lib\javaws.jar;
* E:\Program Files\Java\jre\lib\jce.jar;
* E:\Program Files\Java\jre\lib\jfr.jar;
* E:\Program Files\Java\jre\lib\jfxswt.jar;
* E:\Program Files\Java\jre\lib\jsse.jar;
* E:\Program Files\Java\jre\lib\management-agent.jar;
* E:\Program Files\Java\jre\lib\plugin.jar;E
* :\Program Files\Java\jre\lib\resources.jar;
* E:\Program Files\Java\jre\lib\rt.jar;
* E:\soft\workspace\java\reflection\out\production\reflection;
* D:\Program Files (x86)\IDEA\IntelliJ IDEA 2020.3.2\lib\idea_rt.jar
* */
}
}
4、创建运行时类的对象
5、获取运行类的完整结构
方法:
Class c1 = Class.forName(“cn.doris.reflection.User”); //获取当前对象的Class
//获得类的名字
c1.getName();// 获得包名 + 类名
c1.getSimpleName();// 获得类名
//获得类的属性
c1.getFields();//只能找到public属性
c1.getDeclaredFields();//找到全部的属性
c1.getDeclaredField(“name”); //获得指定属性的值
//获得类的方法
c1.getMethods(); //获得本类及父类的全部public方法
c1.getDeclaredMethods(); //获得本类的所有方法
c1.getMethod(“getName”, null);//获得指定的方法
//获得类的构造器
c1.getConstructors();
c1.getDeclaredConstructors();
c1.getDeclaredConstructor(String.class, int.class, int.class);//获得指定的构造器
package com.bobo.util.reflection.src.com.mao.reflection;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class Test08 {
public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, NoSuchMethodException {
final Class aClass = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.User");
//获得类的名字
System.out.println(aClass.getName()); //com.bobo.util.reflection.src.com.mao.reflection.User 获得包名 + 类名
System.out.println(aClass.getSimpleName()); // User 获得类名
System.out.println("=======================");
//获得类的属性
Field[] fields = aClass.getFields();//只能找到public属性
for (Field field : fields) {
System.out.println("getFields:" + field);
} // 空
fields = aClass.getDeclaredFields();//找到全部的属性
for (Field field : fields) {
System.out.println("getDeclaredFields:" + field);
}
/**
* getDeclaredFields:private java.lang.String com.bobo.util.reflection.src.com.mao.reflection.User.name
* getDeclaredFields:private int com.bobo.util.reflection.src.com.mao.reflection.User.id
* getDeclaredFields:private int com.bobo.util.reflection.src.com.mao.reflection.User.age
* */
//获得指定属性的值
Field name = aClass.getDeclaredField("name");
System.out.println(name);
/**
* private java.lang.String com.bobo.util.reflection.src.com.mao.reflection.User.name
* */
System.out.println("=======================");
//获得类的方法
Method[] methods = aClass.getMethods(); //获得本类及父类的全部public方法
for (Method method : methods) {
System.out.println("getMethods:" + method);
}
/**
* getMethods:public void com.bobo.util.reflection.src.com.mao.reflection.User.setId(int)
* getMethods:public void com.bobo.util.reflection.src.com.mao.reflection.User.setAge(int)
* getMethods:public int com.bobo.util.reflection.src.com.mao.reflection.User.getAge()
* getMethods:public java.lang.String com.bobo.util.reflection.src.com.mao.reflection.User.toString()
* getMethods:public java.lang.String com.bobo.util.reflection.src.com.mao.reflection.User.getName()
* getMethods:public int com.bobo.util.reflection.src.com.mao.reflection.User.getId()
* getMethods:public void com.bobo.util.reflection.src.com.mao.reflection.User.setName(java.lang.String)
* getMethods:public final void java.lang.Object.wait() throws java.lang.InterruptedException
* getMethods:public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
* getMethods:public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
* getMethods:public boolean java.lang.Object.equals(java.lang.Object)
* getMethods:public native int java.lang.Object.hashCode()
* getMethods:public final native java.lang.Class java.lang.Object.getClass()
* getMethods:public final native void java.lang.Object.notify()
* getMethods:public final native void java.lang.Object.notifyAll()
* */
methods = aClass.getDeclaredMethods(); //获得本类的所有方法
for (Method method : methods) {
System.out.println("getDeclaredMethods:" + method);
}
/**
*
getDeclaredMethods:public java.lang.String com.bobo.util.reflection.src.com.mao.reflection.User.toString()
getDeclaredMethods:public java.lang.String com.bobo.util.reflection.src.com.mao.reflection.User.getName()
getDeclaredMethods:public int com.bobo.util.reflection.src.com.mao.reflection.User.getId()
getDeclaredMethods:public void com.bobo.util.reflection.src.com.mao.reflection.User.setName(java.lang.String)
getDeclaredMethods:public void com.bobo.util.reflection.src.com.mao.reflection.User.setId(int)
getDeclaredMethods:public int com.bobo.util.reflection.src.com.mao.reflection.User.getAge()
getDeclaredMethods:public void com.bobo.util.reflection.src.com.mao.reflection.User.setAge(int)
* */
System.out.println("=======================");
//获得指定的方法
//重载
Method getName = aClass.getMethod("getName", null);
Method setName = aClass.getMethod("setName", String.class);
System.out.println(getName); // public java.lang.String com.bobo.util.reflection.src.com.mao.reflection.User.getName()
System.out.println(setName); // public void com.bobo.util.reflection.src.com.mao.reflection.User.setName(java.lang.String)
//获得类的构造器
System.out.println("=======================");
Constructor[] constructors = aClass.getConstructors();
for (Constructor constructor : constructors) {
System.out.println("getConstructors:" + constructor);
}
/**
* getConstructors:public com.bobo.util.reflection.src.com.mao.reflection.User()
* getConstructors:public com.bobo.util.reflection.src.com.mao.reflection.User(java.lang.String,int,int)
* */
constructors = aClass.getDeclaredConstructors();
for (Constructor constructor : constructors) {
System.out.println("getDeclaredConstructors:" + constructor);
}
/**
* getDeclaredConstructors:public com.bobo.util.reflection.src.com.mao.reflection.User()
* getDeclaredConstructors:public com.bobo.util.reflection.src.com.mao.reflection.User(java.lang.String,int,int)
* */
//获得指定的构造器
Constructor declaredConstructor = aClass.getDeclaredConstructor(String.class, int.class, int.class);
System.out.println("指定构造器" + declaredConstructor);
//指定构造器public com.bobo.util.reflection.src.com.mao.reflection.User(java.lang.String,int,int)
}
}
6、调用运行时类的指定结构
6.1 有Class对象,能做什么
6.2 方法及使用
//获得Class对象
Class c1 = Class.forName(“cn.doris.reflection.User”);
//本质上调用了类的无参构造器
User user = (User) c1.newInstance();
//构造器创建对象
Constructor constructor=c1.getDeclaredConstructor(String.class, int.class, int.class);
User user1 = (User) constructor.newInstance(“长歌”,001,17);//invoke:激活
// (对象,“方法值”)
setName.invoke(user2, “doris”);//设置安全检测
name.setAccessible(true);
//动态的创建对象,通过反射
public class Demo11_DynamicCreateObject {
public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException, NoSuchFieldException {
//获得Class对象
Class c1 = Class.forName("cn.doris.reflection.User");
//构造一个对象
/*User user = (User) c1.newInstance();//本质上调用了类的无参构造器
System.out.println(user);*/
//通过构造器创建对象
/*Constructor constructor = c1.getDeclaredConstructor(String.class, int.class, int.class);
User user1 = (User) constructor.newInstance("长歌",001,17);
System.out.println(user1);*/
//通过反射调用普通方法
User user2 = (User) c1.newInstance();
//通过反射获取一个方法
Method setName = c1.getDeclaredMethod("setName", String.class);
//invoke:激活
// (对象,"方法值")
setName.invoke(user2, "doris");
System.out.println(user2.getName());
//通过反射操作属性
User user3 = (User) c1.newInstance();
Field name = c1.getDeclaredField("name");
//不能直接操作私有属性,我们需要关闭程序的安全检测,属性或方法的setAccessible(true)
//设置安全检测
name.setAccessible(true);
name.set(user3, "doris2");
System.out.println(user3.getName());
}
}
6.3 性能检测:
package com.bobo.util.reflection.src.com.mao.reflection;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class Test10 {
// 普通方式调用
public static void test01() {
User user =new User();
long startTime = System.currentTimeMillis();
for (int i = 0; i < 1000000000; i++) {
user.getName();
}
long endTime = System.currentTimeMillis();
System.out.println("普通方式执行10亿次:"+(endTime-startTime)+"ms"); // 普通方式执行10亿次:2ms
}
// 反射方式调用
public static void test02() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
User user =new User();
final Class aClass = user.getClass();
final Method getName = aClass.getDeclaredMethod("getName", null);
long startTime = System.currentTimeMillis();
for (int i = 0; i < 1000000000; i++) {
getName.invoke(user,null);
}
long endTime = System.currentTimeMillis();
System.out.println("反射方式执行10亿次:"+(endTime-startTime)+"ms"); // 反射方式执行10亿次:1904ms
}
// 反射方式调用 关闭检测
public static void test03() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
User user =new User();
final Class aClass = user.getClass();
final Method getName = aClass.getDeclaredMethod("getName", null);
getName.setAccessible(true);
long startTime = System.currentTimeMillis();
for (int i = 0; i < 1000000000; i++) {
getName.invoke(user,null);
}
long endTime = System.currentTimeMillis();
System.out.println("关闭检测方式执行10亿次:"+(endTime-startTime)+"ms"); // 关闭检测方式执行10亿次:1304ms
}
public static void main(String[] args) throws InvocationTargetException, NoSuchMethodException, IllegalAccessException {
test01();
test02();
test03();
}
}
7、反射操作泛型
package com.bobo.util.reflection.src.com.mao.reflection;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;
// 通过反射获取泛型
public class Test11 {
public void test01(Map<String,User>map, List<User>list){
System.out.println("test01");
}
public Map<String,User> test02(){
System.out.println("test02");
return null;
}
public static void main(String[] args) throws NoSuchMethodException {
// 根据反射获取方法
final Method test01 = Test11.class.getMethod("test01", Map.class, List.class); // 获取方法
// 获取方法的参数
final Type[] genericParameterTypes = test01.getGenericParameterTypes(); // 通过方法获取泛型的参数化类型
for (Type genericParameterType : genericParameterTypes) {
System.out.println("#"+genericParameterType); // #java.util.Map<java.lang.String, com.bobo.util.reflection.src.com.mao.reflection.User>
//判断参数是否是参数化类型
if (genericParameterType instanceof ParameterizedType){
//ParameterizedType 表示一种参数化类型,比如Collection<String>
//强转后获取参数化类型
final Type[] actualTypeArguments = ((ParameterizedType) genericParameterType).getActualTypeArguments(); // 强转成参数化类型
for (Type actualTypeArgument : actualTypeArguments) {
// getActualTypeArguments获取真实的参数
System.out.println(actualTypeArgument);
}
}
}
/**
* class java.lang.String
* class com.bobo.util.reflection.src.com.mao.reflection.User
* #java.util.List<com.bobo.util.reflection.src.com.mao.reflection.User>
* class com.bobo.util.reflection.src.com.mao.reflection.User
* */
System.out.println("=========================================================");
Method test02 = Test11.class.getMethod("test02", null);
final Type genericReturnType = test02.getGenericReturnType(); // 通过方法获取泛型返回值类型
if (genericReturnType instanceof ParameterizedType){
final Type[] actualTypeArguments = ((ParameterizedType) genericReturnType).getActualTypeArguments();
for (Type actualTypeArgument : actualTypeArguments) {
System.out.println(actualTypeArgument);
}
}
/**
* class java.lang.String
* class com.bobo.util.reflection.src.com.mao.reflection.User
* */
}
}
8、反射操作注解
package com.bobo.util.reflection.src.com.mao.reflection;
import java.lang.annotation.*;
import java.lang.reflect.Field;
// 练习反射操作注解
public class Test12 {
public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
// 通过反射获取class对象
final Class aClass = Class.forName("com.bobo.util.reflection.src.com.mao.reflection.student02");
// 通过反射获取注解
final Annotation[] annotations = aClass.getAnnotations();
for (Annotation annotation : annotations) {
System.out.println(annotation); // @com.bobo.util.reflection.src.com.mao.reflection.TableHu(value=db_student)
}
// 获取注解的value值
final TableHu annotation = (TableHu) aClass.getAnnotation(TableHu.class);
final String value = annotation.value();
System.out.println(value); //db_student
// 获得类指定的注解
final Field fields = aClass.getDeclaredField("name");
final FieldHu annotation1 = fields.getAnnotation(FieldHu.class);
System.out.println(annotation1.columnName()); // db_name
System.out.println(annotation1.type()); // varchar
System.out.println(annotation1.length()); // 10
}
}
@TableHu("db_student")
class student02{
@FieldHu(columnName = "db_id",type = "int",length = 10)
private int id;
@FieldHu(columnName = "db_age",type = "int",length = 10)
private int age;
@FieldHu(columnName = "db_name",type = "varchar",length = 10)
private String name;
public student02() {
}
public student02(int id, int age, String name) {
this.id = id;
this.age = age;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "student02{" +
"id=" + id +
", age=" + age +
", name='" + name + '\'' +
'}';
}
}
// 类名注解
@Target(ElementType.TYPE) // 类上生效
@Retention(RetentionPolicy.RUNTIME)
@interface TableHu{
String value();
}
@Target(ElementType.FIELD) // 属性上生效
@Retention(RetentionPolicy.RUNTIME)
@interface FieldHu{
String columnName();
String type();
int length();
}