注解和反射

Annotation

	package org.Annotation;
	//什么是注解
	public class Test01 extends Object{
    //@Override 重写的注解
    @Override
    public String toString() {
        return super.toString();
    }
}

内置注解

Override重写父类

	package org.Annotation;

	import java.util.ArrayList;
	import java.util.List;

	//什么是注解
	public class Test01 extends Object{
    //@Override 重写的注解
    @Override
    public String toString() {
        return super.toString();
    }
    //Deprecated    不推荐程序员使用，但是可以使用，或者存在更好的方式
    @Deprecated
    public static void test(){
        System.out.println("Deprecated");
    }

    @SuppressWarnings("all")    //镇压警告
    public  void test02(){
        List list = new ArrayList();
    }

    public static void main(String[] args) {
        test();
    }

}

元注解

	package org.Annotation;

	import java.lang.annotation.*;
	import java.util.EmptyStackException;
	import java.util.EnumMap;

	//测试元注解
	public class Test02 {

    @MyAnnotation
    public void rest(){

    }
	}


	//定义一个注解
	//Target    表示我们的注解可以用在哪些地方

	@Target(value = {ElementType.METHOD,ElementType.TYPE})
	//Retention 表示我们的注解在哪些地方有效
	//runtime>class>sourrces
	@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@interface

package org.Annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

//自定义注解
public class Test03 {
    //注解可以显示赋值，如果没有默认值，我们就必须给注解赋值
    @MyAnnostation2(age = 18,name = "fanxiang")
    public void test(){}

    @MyAnnotation3("fanxiang")
    public void test2(){
    }
}

@Target({ElementType.TYPE,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnostation2{
    //注解的参数：参数类型 + 参数名（）；
    String name() default "";
    int age() default 0;
    int id() default -1;//如果默认值为-1，代表不存在

    String[] schools() default {"西部开源","清华大学"};
}

@Target({ElementType.TYPE,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnotation3{
    String value();
}

反射机制

package org.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 c1 = Class.forName("org.reflection.User");
        System.out.println(c1);

        Class c2 = Class.forName("org.reflection.User");
        Class c3 = Class.forName("org.reflection.User");
        Class c4 = Class.forName("org.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
        System.out.println(c2.hashCode());
        System.out.println(c3.hashCode());
        System.out.println(c4.hashCode());
    }
}

//实体类:pojo entity
class User{
    private String name ;
    private int id ;
    private int age ;

    public User(){
    }

    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 +
                '}';
    }
}

Class类

	package org.reflection;

	//测试class类的创建方式有那些
	public class Test03 {
    public static void main(String[] args) throws ClassNotFoundException {
        Person person = new Student();
        System.out.println("这个人是："+person.name);

        //方式一：通过对象获得
        Class c1 = person.getClass();
        System.out.println(c1.hashCode());

        //方式二：forname获得
        Class c2 = Class.forName("org.reflection.student");
        System.out.println(c2.hashCode());
    }
	}

	class Person{
    public String name;

    public Person(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                '}';
    }
}

	class Student extends Person{
    public Student(){
        this.name = "学生";
    }
}

	class Teacher extends Person{
    public Teacher(){
        this.name = "老师";
    }

}

	 package org.reflection;

	import javax.crypto.interfaces.PBEKey;
	import javax.swing.text.Element;
	import javax.xml.stream.events.Comment;
	import java.lang.annotation.ElementType;

	//所有类型的class对象
	public class Test04 {

    public static void main(String[] args) {
        Class c1 = Object.class;//类
        Class c2 = Comment.class;//接口
        Class c3 = String[].class;//一维数组
        Class c4 = int[][].class;//二位数组
        Class c5 = Override.class;//注解
        Class c6 = ElementType.class;//枚举
        Class c7 = Integer.class;//基本数据类型
        Class c8 = void.class;//void
        Class c9 = Class.class;//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);

        int [] a = new int[10];
        int [] b = new int[100];
        System.out.println(a.getClass().hashCode());
        System.out.println(b.getClass().hashCode());

    }
	}

Java内存分析

方法区是一个特殊的堆

不能主动创建class ,需要做的是获取

	package org.reflection;
	//类如何加载
	  public class Test05 {
    public static void main(String[] args) {
        A a = new A();
        System.out.println(A.m);

        /*
    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;
                        }


        * */
    }
	}

	class A{
    static{
        System.out.println("A类静态代码块初始化");
        m = 300;
    }

        //    m=300
		//    m=100

    static int m = 100;

    public A(){
        System.out.println("A类的无参构造初始化");
    }
	}

康师傅的JVM

分析类的初始化

	package org.reflection;
	//测试类什么时候会初始化
	public class Test06 {

    static {
        System.out.println("Main被加载");
    }

    public static void main(String[] args) throws ClassNotFoundException {
        //1.主动引用
	//        Son son = new Son();

        //反射也会产生主动引用
	//        Class.forName("org.reflection.Son");

	//    不会产生类的引用的方法
	//        System.out.println(Son.b);
	//        通过子类调用父类的方法，子类不会被加载

	//        Son[] array = new Son[5];

	//        所有的常量在连接阶段就存入调用池
        System.out.println(Son.M);
    }
	}


	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 = 300;

    }
    static int m = 100 ;
    static final int M = 1;
	}

类加载器的作用

java的核心rt.jar

	package org.reflection;
	//获取系统类的加载器
	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);

	//    获取系统类加载器的父类加载器-->扩展类加载器
        ClassLoader parent = systemClassLoader.getParent();
        System.out.println(parent);

	//    获取扩展类加载器的父类加载器-->根加载器（C/C++）
        ClassLoader parent1 = parent.getParent();
        System.out.println(parent1);

	//        测试当前类是那个加载器加载的
        ClassLoader classLoader = Class.forName("org.reflection.Test07").getClassLoader();
        System.out.println(classLoader);
	//        测试jdk内置的类是谁加载的
        ClassLoader objectClassLoader  = Class.forName("java.lang.Object").getClassLoader();
        System.out.println(objectClassLoader);

	//        如何获得系统类加载器可以加载的路径
        System.out.printf(System.getProperty("java.class.path"));

	/*
	D:\IDEA\file\Annotation\target\classes
	* */

	//        双亲委派机制
	//        java.lang.Dtring
    }
	}

创建运行时的对象

	package org.reflection;

    import java.lang.reflect.Constructor;
	import java.lang.reflect.Field;
	import java.lang.reflect.Method;

	//获得类的信息
	public class Test08 {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, NoSuchMethodException {
        Class c1 = Class.forName("org.reflection.User");

        User user = new User();
        c1 = user.getClass();
//    获得类的名字
        System.out.println(c1.getName()); //获得包名+类名
        System.out.println(c1.getSimpleName());//获得类名

//    获得类的属性
        System.out.println("============================");
        Field[] fields = c1.getFields();//只能找到public属性

        fields = c1.getDeclaredFields();//可以找到全部的属性
        for (Field field : fields){
            System.out.println(field);
        }

        //获得指定属性的值
        Field name = c1.getDeclaredField("name");
        System.out.println(name);

        //获得类的方法
        System.out.println("=========================");
        //获得本类以及父类的全部public方法
        Method[] methods = c1.getMethods();
        for (Method method : methods){
            System.out.println("正常的："+method);
        }
        //获得本类的所有方法
        methods = c1.getDeclaredMethods();
        for (Method method : methods){
            System.out.println("getDeclaredMethods:"+method);
        }

        //获得指定方法
        //重载
        Method getName = c1.getMethod("getName", null);
        Method setName = c1.getMethod("setName",String.class);
        System.out.println(getName);
        System.out.println(setName);

        //获得指定的构造器
        System.out.println("===================================");
        Constructor[] constructors = c1.getConstructors();
        for (Constructor constructor : constructors) {
            System.out.println(constructor);
            
        }
        constructors = c1.getConstructors();
        for (Constructor constructor : constructors) {
            System.out.println("#"+constructor);

        //获得指定的构造器
            Constructor declaredConstructor = c1.getDeclaredConstructor(String.class, int.class, int.class);
            System.out.println("指定："+declaredConstructor);



        }
    }
}

class的操作：

getname 获取包名+类名
getSimpleName 获取类名
getFields 只能找到public属性
getDeclaredFields 能够找到全部属性
getMethods 获得本类及父类的所有public方法
getDeclareMethods 获得本类的所有方法
Constructor 获得指定的构造器

newInstance 构造一个对象
User user = (User)c1.newInstance();
System.out.println(user);

这个前提是有无参构造器User{}

没有无参，还有一种通过构造器创建对象

getDeclaredConostructor

通过反射获得一个方法

通过反射操作属性

	package org.reflection;

	import java.lang.reflect.Constructor;
	import java.lang.reflect.Field;
	import java.lang.reflect.InvocationTargetException;
	import java.lang.reflect.Method;

	//动态的创建对象，通过反射
	public class Test09 {

    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, InvocationTargetException, NoSuchFieldException {
        //获得Class对象
        Class c1 =  Class.forName("org.reflection.User");

        //构造一个对象
	//        User user = (User)c1.newInstance();//本质上是调用了类的无参构造器
	//        System.out.println(user);

        //通过构造器创造对象
        Constructor constructor = c1.getDeclaredConstructor(String.class, int.class, int.class);
        User user2 = (User) constructor.newInstance("fanx", 001, 33);
        System.out.println(user2);

        //通过反射调用普通方法
        User user3 = (User)c1.newInstance();
        //通过反射获得一个方法
        Method setName = c1.getDeclaredMethod("setName", String.class);
        //invoke:激活的意意思
        //（对象，”方法的值“）
        setName.invoke(user3,"fanxxxx");
        System.out.println(user3.getName());

        //通过反射操作属性
        System.out.println("=============================");
        User user4 = (User)c1.newInstance();
        Field name = c1.getDeclaredField("name");
        //不饿能直接操作私有属性，我们需要关闭程序的安全检测，属性或者方法的setAccessinle(true)
        name.setAccessible(true);
        name.set(user4,"fanx4");
        System.out.println(user4.getName());
    }
}

	package org.reflection;

	import java.lang.reflect.InvocationTargetException;
	import java.lang.reflect.Method;

	//分析性能问题
	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");
    }

    //反射方式调用
    public static void test02() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        User user = new User();
        Class c1 = user.getClass();

        Method getName = c1.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");
    }
    //反射方式调用，关闭检测
    public static void test03() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        User user = new User();
        Class c1 = user.getClass();

        Method getName = c1.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("关闭检测执行10亿次："+(endTime-startTime)+"ms");
    }

    public static void main(String[] args) throws InvocationTargetException, NoSuchMethodException, IllegalAccessException {
        test01();
        test02();
        test03();
    }
	}

反射操作泛型

package org.reflection;

import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
	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{
        Method method = Test11.class.getMethod("test01", Map.class, List.class);

        Type[] genericParameterTypes = method.getGenericParameterTypes();
        for (Type genericParameterType : genericParameterTypes) {
            System.out.println("#"+genericParameterType);
            if(genericParameterType instanceof ParameterizedType){
                Type[] actualTypeArguments = ((ParameterizedType) genericParameterType).getActualTypeArguments();
                for (Type actualTypeArgument : actualTypeArguments) {
                    System.out.println(actualTypeArgument);
                }
            }
        }
    }


	}

反射操作注解

ORM

对象关系映射

	package org.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 {
        Class c1 = Class.forName("org.reflection.Student2");

        //通过反射获得注解
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);

        //获得注解value值
            Tablefan tablefan = (Tablefan)c1.getAnnotation(Tablefan.class);
            String value = tablefan.value();
            System.out.println(value);

        //获得类指定注解的值
            Field f = c1.getDeclaredField("id");
            Fieldfan annotation1 = f.getAnnotation(Fieldfan.class);
            System.out.println(annotation1.columnName());
            System.out.println(annotation1.type());
            System.out.println(annotation1.length());

        }
    }
}
	@Tablefan("db_student")
	class  Student2{

    @Fieldfan(columnName = "db_id",type = "int",length = 10)
    private int id;
    @Fieldfan(columnName = "db_age",type = "int",length = 10)
    private int age;
    @Fieldfan(columnName = "db_name",type = "varchar",length = 3)
    private String name;

    public Student2(){
    }

    public Student2(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 "Stuent2{" +
                "id=" + id +
                ", age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}

	//类名的注解
	@Target(ElementType.TYPE)
	@Retention(RetentionPolicy.RUNTIME)
	@interface Tablefan{
    String value();
}


	//属性的注解
	@Target(ElementType.FIELD)
	@Retention(RetentionPolicy.RUNTIME)
	@interface Fieldfan{
    String columnName();
    String type();
    int length();
	}

posted @ 2025-11-11 14:13 1忧郁女子阅读(0) 评论(0) 收藏举报

刷新页面返回顶部

fan-xxx

注解和反射

注解和反射

内置注解

元注解

自定义注解@interface

反射机制

Class类

Java内存分析

分析类的初始化

类加载器的作用

创建运行时的对象

反射操作泛型

反射操作注解

ORM

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