Java tutorial
/* This program is a part of the companion code for Core Java 8th ed. (http://horstmann.com/corejava) This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. */ import java.lang.reflect.GenericArrayType; import java.lang.reflect.Method; import java.lang.reflect.Modifier; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.lang.reflect.TypeVariable; import java.lang.reflect.WildcardType; import java.util.Arrays; import java.util.Scanner; /** * @version 1.10 2007-05-15 * @author Cay Horstmann */ public class GenericReflectionTest { public static void main(String[] args) { // read class name from command line args or user input String name; if (args.length > 0) name = args[0]; else { Scanner in = new Scanner(System.in); System.out.println("Enter class name (e.g. java.util.Collections): "); name = in.next(); } try { // print generic info for class and public methods Class<?> cl = Class.forName(name); printClass(cl); for (Method m : cl.getDeclaredMethods()) printMethod(m); } catch (ClassNotFoundException e) { e.printStackTrace(); } } public static void printClass(Class<?> cl) { System.out.print(cl); printTypes(cl.getTypeParameters(), "<", ", ", ">", true); Type sc = cl.getGenericSuperclass(); if (sc != null) { System.out.print(" extends "); printType(sc, false); } printTypes(cl.getGenericInterfaces(), " implements ", ", ", "", false); System.out.println(); } public static void printMethod(Method m) { String name = m.getName(); System.out.print(Modifier.toString(m.getModifiers())); System.out.print(" "); printTypes(m.getTypeParameters(), "<", ", ", "> ", true); printType(m.getGenericReturnType(), false); System.out.print(" "); System.out.print(name); System.out.print("("); printTypes(m.getGenericParameterTypes(), "", ", ", "", false); System.out.println(")"); } public static void printTypes(Type[] types, String pre, String sep, String suf, boolean isDefinition) { if (pre.equals(" extends ") && Arrays.equals(types, new Type[] { Object.class })) return; if (types.length > 0) System.out.print(pre); for (int i = 0; i < types.length; i++) { if (i > 0) System.out.print(sep); printType(types[i], isDefinition); } if (types.length > 0) System.out.print(suf); } public static void printType(Type type, boolean isDefinition) { if (type instanceof Class) { Class<?> t = (Class<?>) type; System.out.print(t.getName()); } else if (type instanceof TypeVariable) { TypeVariable<?> t = (TypeVariable<?>) type; System.out.print(t.getName()); if (isDefinition) printTypes(t.getBounds(), " extends ", " & ", "", false); } else if (type instanceof WildcardType) { WildcardType t = (WildcardType) type; System.out.print("?"); printTypes(t.getUpperBounds(), " extends ", " & ", "", false); printTypes(t.getLowerBounds(), " super ", " & ", "", false); } else if (type instanceof ParameterizedType) { ParameterizedType t = (ParameterizedType) type; Type owner = t.getOwnerType(); if (owner != null) { printType(owner, false); System.out.print("."); } printType(t.getRawType(), false); printTypes(t.getActualTypeArguments(), "<", ", ", ">", false); } else if (type instanceof GenericArrayType) { GenericArrayType t = (GenericArrayType) type; System.out.print(""); printType(t.getGenericComponentType(), isDefinition); System.out.print("[]"); } } }