第42天学习打卡（Class类 Class类的常用方法 内存分析 类的加载过程 类加载器 反射操作泛型 反射操作注解）

package com.kuang.reflection;

import java.lang.annotation.*;
import java.lang.reflect.Field;

public class Test12 {
public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
Class c1 = Class.forName(“com.kuang.reflection.Student2”);

    //通过反射获得注解
    Annotation[] annotations = c1.getAnnotations();
    for (Annotation annotation : annotations) {
        System.out.println(annotation);
    }
    //获得注解的value的值
   Tablekuang tablekuang= (Tablekuang)c1.getAnnotation(Tablekuang.class);
    String value = tablekuang.value();
    System.out.println(value);

    //获得类指定的注解
    Field f  = c1.getDeclaredField("id");
    Fieldkuang annotation= f.getAnnotation(Fieldkuang.class);
    System.out.println(annotation.columnName());
    System.out.println(annotation.type());
    System.out.println(annotation.length());
}

}
@Tablekuang(“db_student”)
class Student2 {

@Fieldkuang(columnName = "db_id",type = "int",length = 10)
private int id;
@Fieldkuang(columnName = "db_age",type = "int",length = 10)
private int age;
@Fieldkuang(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 "Student2{" +
            "id=" + id +
            ", age=" + age +
            ", name='" + name + '\'' +
            '}';
}

}

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

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

}