GenericTest

GenericTest.java

import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.HashMap;
import java.util.Map;


public class GenericTest<T1,T2 extends Number> {
	
	private Map<T1 , Integer> map = null;
	
	public static void testParameterizedType() throws NoSuchFieldException, SecurityException{
		
		Type mapGenericType = GenericTest.class.getDeclaredField("map").getGenericType();  //ParameterizedType
		if(mapGenericType instanceof ParameterizedType){
			Type basicType = ((ParameterizedType) mapGenericType).getRawType();
			

			System.out.println("basicType equals Map.class is " + (basicType ==Map.class)); //返回True
			
			System.out.println("基本类型为："+basicType);  //Map
			// 获取泛型类型的泛型参数, 分别为 T1, class java.lang.Integer
			Type[] types = ((ParameterizedType) mapGenericType).getActualTypeArguments();
			for (int i = 0; i < types.length; i++) {
				System.out.println("第"+(i+1)+"个泛型类型是："+types[i]);
			}
			
			System.out.println(((ParameterizedType) mapGenericType).getOwnerType());  //null
		}
	}
	
	
	public static void testTypeVariable() throws NoSuchFieldException, SecurityException{
		
		Type mapGenericType = GenericTest.class.getDeclaredField("map").getGenericType();  //ParameterizedType
		if(mapGenericType instanceof ParameterizedType){
			// 获取泛型类型的泛型参数, 分别为 T1, class java.lang.Integer
			Type[] types = ((ParameterizedType) mapGenericType).getActualTypeArguments();
			for (int i = 0; i < types.length; i++) {
				if( types[i] instanceof TypeVariable){
					// T1 is TypeVariable, and Integer is not.
					System.out.println("the "+(i+1)+"th is TypeVariable");
				}else{
					System.out.println("the "+(i+1)+"th is not TypeVariable");
				}
			}
			
		}
		
		System.out.println("GenericTest TypeVariable");
		
		TypeVariable<Class<GenericTest>>[] typeVariables = GenericTest.class.getTypeParameters();
		
		// console print  T1, T2
		for(TypeVariable tmp : typeVariables){
			System.out.println(""+tmp);
			Type[] bounds = tmp.getBounds(); //return upper bounds
			if(bounds.length > 0){ 
				//T2 has upper bounds which is class java.lang.Number, 
				//T1's upper bounds is Object which is default.
				System.out.println("bounds[0] is: "+bounds[0]);
			}
			
			System.out.println("name is: "+tmp.getName());  //  T1, T2
			System.out.println("GenericDeclaration is equals GenericTest.class: "+ (tmp.getGenericDeclaration()==GenericTest.class)); //GenericTest
		}
	}
	
	
	private Map<? extends Number, ? super Integer> map1 = new HashMap<Integer,Integer>();
	public static void testWildcardType() throws NoSuchFieldException, SecurityException{
		Type mapGenericType = GenericTest.class.getDeclaredField("map1").getGenericType();
		TypeVariable<Class<GenericTest>>[] typeVariables = GenericTest.class.getTypeParameters();
		Type[] types = ((ParameterizedType) mapGenericType).getActualTypeArguments();
		for(Type t : types){
			if(t instanceof WildcardType){
				System.out.println("wildcardType");
				
				if( ((WildcardType) t).getLowerBounds().length > 0 )
				System.out.println((((WildcardType) t).getLowerBounds())[0]); //print java.lang.Integer
				
				if( ((WildcardType) t).getUpperBounds().length > 0 )
					System.out.println((((WildcardType) t).getUpperBounds())[0]); //print java.lang.Number, Object
					
			}
		}
	}
	
	
	private T1[] tArray = null;
	public static void testGenericArrayType() throws NoSuchFieldException, SecurityException{
		Type tArrayGenericType = GenericTest.class.getDeclaredField("tArray").getGenericType();
		if(tArrayGenericType instanceof GenericArrayType){
			System.out.println("is GenericArrayType");  //
			Type t1 = ((GenericArrayType) tArrayGenericType).getGenericComponentType();
			System.out.println(t1);   // print T1
			if( t1 instanceof TypeVariable){
				System.out.println("t1 is TypeVariable");
				System.out.println(((TypeVariable) t1).getGenericDeclaration());
			}
		}
	}
	public static void main(String[] args) throws SecurityException, NoSuchFieldException {
		testParameterizedType();
		testTypeVariable();
		testWildcardType();
		testGenericArrayType();
	}
	
}