Java核心技術很優美的代碼2 "萬能的"toString

/**
   @version 1.11 2004-02-21
   @author Cay Horstmann
*/

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

public class ObjectAnalyzerTest
{  
   public static void main(String[] args)
   { 
      ArrayList<Integer> squares = new ArrayList<Integer>();
      for (int i = 1; i <= 5; i++) squares.add(i * i);
      System.out.println(new ObjectAnalyzer().toString(squares));
   }
}

class ObjectAnalyzer
{
   /**
      Converts an object to a string representation that lists 
      all fields. 
      @param obj an object
      @return a string with the object's class name and all
      field names and values
   */
   public String toString(Object obj)
   {  
      if (obj == null) return "null";
      if (visited.contains(obj)) return "...";
      visited.add(obj);
      Class cl = obj.getClass();
      if (cl == String.class) return (String) obj;
      if (cl.isArray())
      {
         String r = cl.getComponentType() + "[]{";
         for (int i = 0; i < Array.getLength(obj); i++)
         {
            if (i > 0) r += ",";
            Object val = Array.get(obj, i);
            if (cl.getComponentType().isPrimitive()) r += val;
            else r += toString(val);            
         }
         return r + "}";
      }

      String r = cl.getName();
      // inspect the fields of this class and all superclasses
      do
      {
         r += "[";
         Field[] fields = cl.getDeclaredFields();
         AccessibleObject.setAccessible(fields, true);
         // get the names and values of all fields
         for (Field f : fields)
         {  
            if (!Modifier.isStatic(f.getModifiers()))
            {
               if (!r.endsWith("[")) r += ",";
               r += f.getName() + "=";
               try
               {  
                  Class t = f.getType();
                  Object val = f.get(obj);
                  if (t.isPrimitive()) r += val;
                  else r += toString(val);
               } 
               catch (Exception e) { e.printStackTrace(); }
            }
         }
         r += "]";
         cl = cl.getSuperclass();
      }
      while (cl != null);

      return r;
   }

   private ArrayList<Object> visited = new ArrayList<Object>();
}