这是我参与11月更文挑战的第26天，活动详情查看：2021最后一次更文挑战
- Parameterized Type : 表示一种参数化类型，比如Collection，String是参数化类型
- GenericArray Type:表示一种元素类型是参数化类型或者类型变量的数组类型
- TypeVariable：是各种类型变量的公共父接口
- WildcardType ：代表一种通配符类型表达式
package refection;
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 Test10 {
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 {
// 通过反射获取方法
Method method = Test10.class.getDeclaredMethod("test01", Map.class, List.class);
// 通过反射获取参数信息
Type []type = method.getGenericParameterTypes();
for (Type type1 : type) {
System.out.println("#" + type1);
//如果获取到的这个泛型是 ParameterizedType ， 那么进行进行强转 ， 然后输出
if(type1 instanceof ParameterizedType){
// 整体打印（针对于多个泛型参数的集合的方法而言）
// System.out.println(type1);
// 分别打印(针对于多个泛型参数的集合的方法而言)
Type []types = ((ParameterizedType)type1).getActualTypeArguments();
for (Type type2 : types) {
System.out.println(type2);
}
}
}
}
}
2.12 获取注解信息
练习ORM
package refection;
import java.lang.annotation.*;
import java.lang.reflect.Field;
import java.util.Objects;
@SuppressWarnings("all")
public class Test11 {
public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
Class c1 = Class.forName("refection.Student2");
// 通过反射获得注解
Annotation[]annotations = c1.getAnnotations();
for (Annotation annotation : annotations) {
System.out.println(annotation);
}
// 通过注解获得value的值
Table table = (Table)c1.getAnnotation(Table.class);
String value = table.value();
System.out.println(value);
// 获得指定的注解
Field f = c1.getDeclaredField("name");
File annotation = f.getAnnotation(File.class);
System.out.println(annotation.columnName());
}
}
@Table("db_student")
class Student2{
@File(columnName = "db_name" , type = "varchar" , length = 3)
private String name ;
@File(columnName = "db_id" , type = "int " , length = 10)
private int id ;
@File(columnName = "db_age" , type = "int " , length = 10)
private int age ;
public Student2() {
}
public Student2(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 "Student2{" +
"name='" + name + ''' +
", id=" + id +
", age=" + age +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
refection.Student2 student2 = (refection.Student2) o;
return id == student2.id &&
age == student2.age &&
Objects.equals(name, student2.name);
}
@Override
public int hashCode() {
return Objects.hash(name, id, age);
}
}
// 类名的注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface Table{
String value();
}
// 属性的注解
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface File{
String columnName() ;
String type();
int length();
}
