Type是Java 编程语言中所有类型的公共高级接口,和Object不同,Object是所有类的父类,即Object是Type的父类。
原始类型(Class):不仅仅包含我们平常所指的类,还包括枚举、数组、注解等;
参数化类型(ParameterizedType):就是我们平常所用到的泛型List、Map;
数组类型(GenericArrayType):并不是我们工作中所使用的数组String[] 、byte[],而是带有泛型的数组,即T[] ;
基本类型(Class):也就是我们所说的java的基本类型,即int,float,double等。
/** * * ParameterizedType表示参数化类型,也就是泛型,例如List<T>、Set<T>等; **/ private List<T> list=null; private List<T> set=null; @Test public void test() throws NoSuchFieldException { Field fieldList=ParameterizedTypeDemo.class.getDeclaredField("list"); Type typeList = fieldList.getGenericType(); //sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl System.out.println("获取的type类型 typeList-->"+typeList.getClass().getName()); Field fieldSet=ParameterizedTypeDemo.class.getDeclaredField("set"); Type typeSet = fieldSet.getGenericType(); //sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl System.out.println("获取的type类型 typeSet-->"+typeSet.getClass().getName()); } private Map<String,Integer> map=null; @Test public void tset2() throws NoSuchFieldException { Field declaredField = ParameterizedTypeDemo.class.getDeclaredField("map"); Type genericType = declaredField.getGenericType(); ParameterizedType parameterizedType=(ParameterizedType)genericType; Type name1 = parameterizedType.getActualTypeArguments()[0]; //java.lang.String System.out.println("ParameterizedType 获取参数1泛型类全名-->"+name1.getTypeName()); Type name2 = parameterizedType.getActualTypeArguments()[1]; //java.lang.Integer System.out.println("ParameterizedType 获取参数2泛型类全名-->"+((Class)name2).getName()); Type rawType = parameterizedType.getRawType(); //interface java.util.Map System.out.println("获取声明泛型的类或者接口---》"+rawType); }
private List<T> list; /** * 泛型的类型变量,指的是List<T>、Map<K,V>中的T,K,V等值,实际的Java类型是TypeVariableImpl * (TypeVariable的子类);此外,还可以对类型变量加上extend限定,这样会有类型变量对应的上限; * **/ @Test public void test() throws NoSuchFieldException { Field list = TypeVariableDemo.class.getDeclaredField("list"); //获取该属性的实际类型 Type genericType = list.getGenericType(); ParameterizedType parameterizedType=(ParameterizedType)genericType; //获取泛型中的实际类型 Type[] actualTypeArguments = parameterizedType.getActualTypeArguments(); //sun.reflect.generics.reflectiveObjects.TypeVariableImpl System.out.println("获取泛型中的实际类型-->"+actualTypeArguments[0].getClass().getName()); } @Test public void test2() throws NoSuchFieldException { new TypeVariableTwoDemo().test(); } public class TypeVariableTwoDemo<T extends Number & Serializable & Comparable,K>{ private T t; private K k; public void test() throws NoSuchFieldException { Field field = TypeVariableTwoDemo.class.getDeclaredField("t"); Type genericType = field.getGenericType(); TypeVariable typeVariable=(TypeVariable)genericType; Type[] bounds = typeVariable.getBounds(); //class java.lang.Number //interface java.io.Serializable //interface java.lang.Comparable Arrays.stream(bounds).forEach(s-> System.out.println("获取类型变量的上界-->"+s)); Field field2 = TypeVariableTwoDemo.class.getDeclaredField("k"); Type genericType2 = field2.getGenericType(); TypeVariable typeVariable2=(TypeVariable)genericType2; Type[] bounds2 = typeVariable2.getBounds(); //class java.lang.Object Arrays.stream(bounds2).forEach(s-> System.out.println("获取类型变量的上界-->"+s)); //class com.yxkj.other.modular.reflection.type.TypeVariableDemo$TypeVariableTwoDemo System.out.println("获取声明该类型变量实体-->"+typeVariable2.getGenericDeclaration()); //K System.out.println("获取声明该类型变量实体-->"+typeVariable2.getName()); } }
private T[] t; private List<String>[] listArray; /** * 泛型数组类型,例如List<String>[] 、T[]等; * **/ @Test public void test() throws NoSuchFieldException { Field t = GenericArraytypeDemo.class.getDeclaredField("t"); Type genericType = t.getGenericType(); //sun.reflect.generics.reflectiveObjects.GenericArrayTypeImpl System.out.println("获取Type的实际类型-->"+genericType.getClass().getName()); } @Test public void test2() throws NoSuchFieldException { Field t = GenericArraytypeDemo.class.getDeclaredField("listArray"); Type genericType = t.getGenericType(); GenericArrayType genericType1 = (GenericArrayType) genericType; Type genericComponentType = genericType1.getGenericComponentType(); //java.util.List<java.lang.String> System.out.println("获取listArray的实际类型-->"+genericComponentType); }
在程序运行期间,每一个类都对应一个Class对象,这个对象包含了类的修饰符、方法,属性、构造等信息,所以我们可以对这个Class对象进行相应的操作,这就是Java的反射;
*代码:
private ClassDemo classDemo; /** * * 在Java中,每个.class文件在程序运行期间,都对应着一个Class对象, * 这个对象保存有这个类的全部信息;因此,Class对象也称之为Java反射的基础 * **/ @Test public void test() throws NoSuchFieldException { Field field = ClassDemo.class.getDeclaredField("classDemo"); Type genericType = field.getGenericType(); //class com.yxkj.other.modular.reflection.type.ClassDemo System.out.println("获取Type原始类型-->"+genericType); }
private List<? extends Number> listNum; private List<? super String> listStr; /** * * ?---通配符表达式,表示通配符泛型,但是WildcardType并不属于Java-Type中的一钟; * 例如:List<? extends Number> 和 List<? super Integer>; * **/ @Test public void test() throws NoSuchFieldException { Field declaredField = WildcardTypeDemo.class.getDeclaredField("listNum"); Type genericType = declaredField.getGenericType(); ParameterizedType parameterizedType=(ParameterizedType)genericType; //获取泛型中的实际类型 Type[] actualTypeArguments = parameterizedType.getActualTypeArguments(); //class sun.reflect.generics.reflectiveObjects.WildcardTypeImpl System.out.println("获取泛型中的实际类型-->"+actualTypeArguments[0].getClass()); WildcardType wildcardType= (WildcardType)actualTypeArguments[0]; Type[] upperBounds = wildcardType.getUpperBounds(); System.out.println("获取泛型变量的上边界-->"+upperBounds[0]); Field declaredFieldlowerBounds = WildcardTypeDemo.class.getDeclaredField("listStr"); Type genericTypelowerBounds = declaredFieldlowerBounds.getGenericType(); ParameterizedType parameterizedTypelowerBounds=(ParameterizedType)genericTypelowerBounds; //获取泛型中的实际类型 Type[] actualTypeArgumentslowerBounds = parameterizedTypelowerBounds.getActualTypeArguments(); WildcardType wildcardTypelowerBounds= (WildcardType)actualTypeArgumentslowerBounds[0]; Type[] lowerBounds = wildcardTypelowerBounds.getLowerBounds(); System.out.println("获取泛型变量的下边界-->"+lowerBounds[0]); }
https://gitee.com/zhuayng/foundation-study/tree/develop/JavaBasis/Other/src/main/java/com/yxkj/other/modular/reflection/type
https://www.cnblogs.com/linghu-java/p/8067886.html