Java核心技术卷I程序清单5-14及5-15

P200
程序清单5-14 objectAnalyzer/ObjectAnalyzerTest.java

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import java.util.ArrayList;

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

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P200
程序清单5-15 objectAnalyzer/ObjectAnalyzer.java

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1. 代码
2. 分析
3. 重要API

1.代码

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;

public class ObjectAnalyzer
{
   
   private ArrayList<Object> visited = new ArrayList<>();

   /**
    * 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";//false
      if (visited.contains(obj)) return "...";//false
      visited.add(obj);
      Class cl = obj.getClass();
      if (cl == String.class) return (String) obj;//false
      if (cl.isArray())//true
      {
    //获取cl数组的Class对象
         String r = cl.getComponentType() + "[]{";
         for (int i = 0; i < Array.getLength(obj); i++)
         {
            if (i > 0) r += ",";
            Object val = Array.get(obj, i);

    //判断cl数组的Class对象是否为原始类型
            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 += "[";
    getDeclaredFields请参考程序清单5-13
         Field[] fields = cl.getDeclaredFields();

    //将fields的 accessible 标志设置为指示的布尔值。值为 true 则指示反射的对象在使用时应该取消 Java 语言访问检查。值为 false 则指示反射的对象应该实施 Java 语言访问检查。 
         AccessibleObject.setAccessible(fields, true);
         // get the names and values of all fields
         for (Field f : fields)
         {
    //Modifier.isStatic请参考程序清单5-13
            if (!Modifier.isStatic(f.getModifiers()))
            {
               if (!r.endsWith("[")) r += ",";
               r += f.getName() + "=";
               try
               {
               //获取f的类型