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Java获取泛型T的类型 T.class
2025-10-05 10:26:44 资源战场
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
public class Main{
public static void main(String[] args)
{
Foo
foo = new Foo (){}; // 在类的外部这样获取
Type type = ((ParameterizedType)foo.getClass().getGenericSuperclass()).getActualTypeArguments()[0];
System.out.println(type);
// 在类的内部这样获取
System.out.println(foo.getTClass());
}
}
abstract class Foo
{ public Class
getTClass() {
Class
tClass = (Class )((ParameterizedType)getClass().getGenericSuperclass()).getActualTypeArguments()[0]; return tClass;
}
}
输出:
class java.lang.String
class java.lang.String
上面的代码不是万能的,只有实例化T的子类才能按上述方法获得T的实际类型, 如果子类没有实例化T,则无法获取T的实际类型; 比如,class Child 并没有实例化T,所以得不到String.class;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
public class Main{
public static void main(String[] args){
//区别在new Child
()没有{}匿名类 Foo
foo = new Child (); // 在类的外部这样获取
Type type = ((ParameterizedType)foo.getClass().getGenericSuperclass()).getActualTypeArguments()[0];
System.out.println(type);
// 在类的内部这样获取
System.out.println(foo.getTClass());
}
}
abstract class Foo
{ public Class
getTClass() {
Class
tClass = (Class )((ParameterizedType)getClass().getGenericSuperclass()).getActualTypeArguments()[0]; return tClass;
}
}
class Child
extends Foo { }
输出：
Exception in thread "main" java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType
at com.hankcs.Main.main(Main.java:9)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
有一种解决方式,父类本身不获取泛型的具体类型,仅提供抽象方法,由子类来提供具体的类型
public abstract class Foo
{ public abstract Class getEntityClass();
}
public class Child extends Foo
{ public Class getEntityClass() {
return String.class;
}
}
对于获取泛型的方法,比较完整的代码如下:
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
public class GenericsUtils {
/**
* 通过反射,获得定义Class时声明的父类的范型参数的类型. 如public BookManager extends
* GenricManager
*
* @param clazz The class to introspect
* @return the first generic declaration, or
Object.classif cannot be determined*/
public static Class getSuperClassGenricType(Class clazz) {
return getSuperClassGenricType(clazz, 0);
}
/**
* 通过反射,获得定义Class时声明的父类的范型参数的类型. 如public BookManager extends GenricManager
*
* @param clazz clazz The class to introspect
* @param index the Index of the generic ddeclaration,start from 0.
*/
public static Class getSuperClassGenricType(Class clazz, int index)
throws IndexOutOfBoundsException {
Type genType = clazz.getGenericSuperclass();
if (!(genType instanceof ParameterizedType)) {
return Object.class;
}
Type[] params = ((ParameterizedType) genType).getActualTypeArguments();
if (index >= params.length || index < 0) {
return Object.class;
}
if (!(params[index] instanceof Class)) {
return Object.class;
}
return (Class) params[index];
}
}
转载来源: http://blog.csdn.net/wangjunjun2008/article/details/43970217 http://www.hankcs.com/program/t-class.html https://www.cnblogs.com/sirab415/p/6133533.html