反射+Class類方法_利用反射分析類的能力

小知識點：obj.getClass().getName()--Class類方法getName()獲得物件所屬類的類名字串

反射機制最重要的內容--檢查類的結構（一般編寫應用程式用很少，而編寫應用工具用較多）

import java.util.*;
import java.lang.reflect.*;

/**
 * This program uses reflection to print all features of a class.
 * @version 1.1 2004-02-21
 * @author Cay Horstmann
 */
public class ReflectionTest
{
   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.Date): ");
         name = in.next();
      }

      try
      {
         // print class name and superclass name (if != Object)
         Class cl = Class.forName(name);
         Class supercl = cl.getSuperclass();
         String modifiers = Modifier.toString(cl.getModifiers());
         if (modifiers.length() > 0) System.out.print(modifiers + " ");
         System.out.print("class " + name);
         if (supercl != null && supercl != Object.class) System.out.print(" extends "
               + supercl.getName());

         System.out.print("\n{\n");
         printConstructors(cl);
         System.out.println();
         printMethods(cl);
         System.out.println();
         printFields(cl);
         System.out.println("}");
      }
      catch (ClassNotFoundException e)
      {
         e.printStackTrace();
      }
      System.exit(0);
   }

   /**
    * Prints all constructors of a class
    * @param cl a class
    */
   public static void printConstructors(Class cl)
   {
      Constructor[] constructors = cl.getDeclaredConstructors();

      for (Constructor c : constructors)
      {
         String name = c.getName();
         System.out.print("   ");
         String modifiers = Modifier.toString(c.getModifiers());
         if (modifiers.length() > 0) System.out.print(modifiers + " ");         
         System.out.print(name + "(");

         // print parameter types
         Class[] paramTypes = c.getParameterTypes();
         for (int j = 0; j < paramTypes.length; j++)
         {
            if (j > 0) System.out.print(", ");
            System.out.print(paramTypes[j].getName());
         }
         System.out.println(");");
      }
   }

   /**
    * Prints all methods of a class
    * @param cl a class
    */
   public static void printMethods(Class cl)
   {
      Method[] methods = cl.getDeclaredMethods();

      for (Method m : methods)
      {
         Class retType = m.getReturnType();
         String name = m.getName();

         System.out.print("   ");
         // print modifiers, return type and method name
         String modifiers = Modifier.toString(m.getModifiers());
         if (modifiers.length() > 0) System.out.print(modifiers + " ");         
         System.out.print(retType.getName() + " " + name + "(");

         // print parameter types
         Class[] paramTypes = m.getParameterTypes();
         for (int j = 0; j < paramTypes.length; j++)
         {
            if (j > 0) System.out.print(", ");
            System.out.print(paramTypes[j].getName());
         }
         System.out.println(");");
      }
   }

   /**
    * Prints all fields of a class
    * @param cl a class
    */
   public static void printFields(Class cl)
   {
      Field[] fields = cl.getDeclaredFields();

      for (Field f : fields)
      {
         Class type = f.getType();
         String name = f.getName();
         System.out.print("   ");
         String modifiers = Modifier.toString(f.getModifiers());
         if (modifiers.length() > 0) System.out.print(modifiers + " ");         
         System.out.println(type.getName() + " " + name + ";");
      }
   }
}

output：

Enter class name (e.g. java.util.Date): 
java.util.Date
public class java.util.Date
{
   public java.util.Date(int, int, int, int, int, int);
   public java.util.Date(java.lang.String);
   public java.util.Date();
   public java.util.Date(long);
   public java.util.Date(int, int, int);
   public java.util.Date(int, int, int, int, int);

   public boolean after(java.util.Date);
   public boolean before(java.util.Date);
   public boolean equals(java.lang.Object);
   public java.lang.String toString();
   public int hashCode();
   public java.lang.Object clone();
   public int compareTo(java.util.Date);
   public volatile int compareTo(java.lang.Object);
   private void readObject(java.io.ObjectInputStream);
   private void writeObject(java.io.ObjectOutputStream);
   private final sun.util.calendar.BaseCalendar$Date normalize();
   private final sun.util.calendar.BaseCalendar$Date normalize(sun.util.calendar.BaseCalendar$Date);
   public static long parse(java.lang.String);
   public static long UTC(int, int, int, int, int, int);
   public long getTime();
   private static final java.lang.StringBuilder convertToAbbr(java.lang.StringBuilder, java.lang.String);
   private final sun.util.calendar.BaseCalendar$Date getCalendarDate();
   private static final sun.util.calendar.BaseCalendar getCalendarSystem(long);
   private static final sun.util.calendar.BaseCalendar getCalendarSystem(sun.util.calendar.BaseCalendar$Date);
   private static final sun.util.calendar.BaseCalendar getCalendarSystem(int);
   public int getDay();
   public int getHours();
   private static final synchronized sun.util.calendar.BaseCalendar getJulianCalendar();
   static final long getMillisOf(java.util.Date);
   public int getMinutes();
   public int getMonth();
   public int getSeconds();
   private final long getTimeImpl();
   public int getTimezoneOffset();
   public int getYear();
   public void setDate(int);
   public void setHours(int);
   public void setMinutes(int);
   public void setMonth(int);
   public void setSeconds(int);
   public void setYear(int);
   public java.lang.String toGMTString();
   public java.time.Instant toInstant();
   public java.lang.String toLocaleString();
   public int getDate();
   public static java.util.Date from(java.time.Instant);
   public void setTime(long);

   private static final sun.util.calendar.BaseCalendar gcal;
   private static sun.util.calendar.BaseCalendar jcal;
   private transient long fastTime;
   private transient sun.util.calendar.BaseCalendar$Date cdate;
   private static int defaultCenturyStart;
   private static final long serialVersionUID;
   private static final [Ljava.lang.String; wtb;
   private static final [I ttb;
}