Java 核心技术（第八版）卷1：基础知识：例5-7P193ObjectAnalyzerTest

这个程序我实现了，但是运行不了，有问题。留待这里的大佬们给看看。

import java.lang.reflect.*;
import java.util.*;
//本程序演示 使用反射来在对象上从事间谍活动，刺探一些关于object的信息
public class ObjectAnalyzerTest {
    public static void main(String [] args)
    {
        ArrayList squares=new ArrayList();
        for(int i=1;i<=5;i++)
           squares.add(i*i);
        System.out.println(new ObjectAnalyzer().toString(squares));
    }
}
class ObjectAnalyzer
{
    //转换一个对象到字符串 代表着 需要列出所有的字段
    //obj 参数 是一个对象
    //返回一个string 是对象的类名和所有字段的名字和值
    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()+"[]{";//getComponentType():Returns the Class representing the component
            // type of an array.If this class does not represent an array class this method returns null.
            for(int i=0;i0) r+=",";
                Object val=Array.get(obj,i);//Returns the value of the indexed component in the specified array object.
                // The value is automatically wrapped in an object if it has a primitive type.
                if(cl.getComponentType().isPrimitive()) r+=val;//如果是基本数据类型，r=r+val;
                else r+=toString(val);//如果不是基本类型，就调用toString（）方法
            }
            return r+"}";
        }
        String r=cl.getName();
        //检查这个类和所有超类的字段
        do
        {
            r+="[";
            Field[] fields=cl.getDeclaredFields();
            AccessibleObject.setAccessible(fields,true);
            //得到所有字段的 name 和 value
            for(Field f:fields)
            {
                if(!Modifier.isStatic(f.getModifiers()))
                {
                    if(!r.endsWith("["))r+=",";
                    r+=f.getName()+"=";
                    try
                    {
                        Class t=f.getType();  //Returns a Class object that identifies the declared type for the field
                                              // represented by this Field object.
                        Object val=f.get(obj);//Returns the value of the field represented by this Field, on the specified object.
                                              // The value is automatically wrapped in an object if it has a primitive type.
                        if(t.isPrimitive()) r+=val;
                        else r+=toString(val);
                    }
                    catch (Exception e)
                    {
                        e.printStackTrace();//Prints this throwable and its backtrace to the standard error stream.
                        // This method prints a stack trace for this Throwable object on the error output stream
                        // that is the value of the field System.err.
                    }
                }
            }
            r+="]";
            cl=cl.getSuperclass();
        }
        while(cl!=null);
            return  r;
    }
    private ArrayList