Java泛型获取测试（父类，接口，类属性-List T，Map T）

素颜马尾好姑娘i 2021-06-24 14:36 319阅读 0赞

package generic;
    
    import org.apache.poi.ss.formula.functions.T;
    
    import java.lang.reflect.ParameterizedType;
    import java.lang.reflect.Type;
    import java.lang.reflect.TypeVariable;
    import java.lang.reflect.WildcardType;
    import java.util.ArrayList;
    import java.util.List;
    
    /**
     * Created by Administrator on 2017/1/10.
     */
    class Parent<T>{
        public Class<T> instance;
        public Parent(){
    
        }
    }
    
    interface GenericInterface<T> {
        final int b =1;
        static final int c =43;
        static double d=2;
        //abstract void a();
    }
    
    interface WildInterface<T extends Number> {
    }
    
    public class GenericTest extends Parent<Integer> implements GenericInterface<Double>,WildInterface<Integer>{
        public List<String> real = new ArrayList<>();
        public List<? extends Number> real2 = new ArrayList<>();
        public List real3 = new ArrayList();
        public static void main(String[] args) throws NoSuchFieldException {
            GenericTest test = new GenericTest();
            Type type = test.getClass().getGenericSuperclass();
            System.out.println(type.toString());
    
            System.out.println("parent class ----------------------------------------------");
            if(type instanceof ParameterizedType){
                for(Type t : ((ParameterizedType) type).getActualTypeArguments()){
                    System.out.println(t.toString());
                    System.out.println(((Class)t).getCanonicalName());
                }
            }
    
            System.out.println();
            System.out.println("interface class ----------------------------------------------");
            //interface
            for (Type t : test.getClass().getGenericInterfaces()) {
                Type[] temp = ((ParameterizedType) t).getActualTypeArguments();
                for (Type c : temp) {
                    if(c instanceof WildcardType){
                        System.out.println("wild：" +((WildcardType) c).getUpperBounds().toString());
                    }
                    System.out.println(c);
                    System.out.println(((Class) c).getName());
                }
    
            }
    
            //这个list只能是成员变量或方法变量中才能获得他的泛型。
            //can not get
            System.out.println();
            System.out.println("list class ----------------------------------------------");
            List<String> list = new ArrayList<String>();
            Type lType = list.getClass().getGenericSuperclass();
            System.out.println(lType.toString());
            if(lType instanceof ParameterizedType){
                for(Type t : ((ParameterizedType) lType).getActualTypeArguments()){
                    System.out.println(t.toString());
                    //System.out.println(((Class)t).getCanonicalName());
                }
            }
    
            //get
            System.out.println();
            System.out.println("list field ----------------------------------------------");
            lType = test.getClass().getField("real").getGenericType();
            System.out.println(lType.toString());
            if(lType instanceof ParameterizedType){
                for(Type t : ((ParameterizedType) lType).getActualTypeArguments()){
                    System.out.println(t.toString());
                    //System.out.println(((Class)t).getCanonicalName());
                }
            }
    
            System.out.println();
            System.out.println("list field WildcardType ----------------------------------------------");
            lType = test.getClass().getField("real2").getGenericType();
            System.out.println(lType.toString());
            if(lType instanceof ParameterizedType){
                for(Type t : ((ParameterizedType) lType).getActualTypeArguments()){
                    System.out.println(t.toString());
                    System.out.println(((WildcardType)t).getUpperBounds()[0]);
                    //System.out.println(((Class)t).getCanonicalName());
                }
            }
    
            System.out.println();
            System.out.println("class TypeVariable ----------------------------------------------");
            TypeVariable[] v  = test.getClass().getSuperclass().getTypeParameters();
            for (TypeVariable vv : v) {
                System.out.println(vv.getName());
                Type[] tt = vv.getBounds();
                for (Type c : tt) {
                    System.out.println(((Class) c).getName());
                }
            }
    
        }
    }

输出：

generic.Parent<java.lang.Integer>  
parent class ----------------------------------------------  
class java.lang.Integer  
java.lang.Integer  
  
  
interface class ----------------------------------------------  
class java.lang.Double  
java.lang.Double  
class java.lang.Integer  
java.lang.Integer  
  
  
list class ----------------------------------------------  
java.util.AbstractList<E>  
E  
  
  
list field ----------------------------------------------  
java.util.List<java.lang.String>  
class java.lang.String  
  
  
list field WildcardType ----------------------------------------------  
java.util.List<? extends java.lang.Number>  
? extends java.lang.Number  
class java.lang.Number  
  
  
class TypeVariable ----------------------------------------------  
T  
java.lang.Object