开源：对象运行时大小参考实现(sizeof)

支持递归引用，唯一不支持的就是不等长数组，不过要支持这个也不难，两个原因不改进它：
1.大部分数组都是等长的。
2.这个东西实在没看出有什么实际应用，这个是主要原因。
需要读者对反射和数组有比较深的认识：

package treeroot.util;

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

/**
 * Compute the size of a Runtime object or Primitive type.
 * Because the memory allocation is unknown,we just add
 * all the fields size of a object.
 * the primitive size is thounght as
 * boolean:1
 * byte:1
 * short:2
 * char:2
 * int:4
 * float:4
 * long:8
 * double:8
 * the array size are the sum of all the elements
 * the null reference is thought to 4 byte.
 * the Object instance has the size 8.
 *
 */
public class Size
{
 final private static int BOOLEAN=1;
 final private static int BYTE=1;
 final private static int SHORT=2;
 final private static int CHAR=2;
 final private static int INT=4;
 final private static int FLOAT=4;
 final private static int LONG=8;
 final private static int DOUBLE=8;
 final private static int REFERENCE=4;
 final private static int OBJECT=8;
 
 private static ThreadLocal objs=new ThreadLocal();
 private static void init(Object o){
  Map map=new IdentityHashMap();
  map.put(o,null);
  objs.set(map);
 }

 public static int sizeof(boolean i){
  return BOOLEAN;
 }
 public static int sizeof(byte b){
  return BYTE;
 }
 public static int sizeof(short s){
  return SHORT;
 }
 public static int sizeof(char c){
  return CHAR;
 }
 public static int sizeof(int i){
  return INT;
 }
 public static int sizeof(float f){
  return FLOAT;
 }
 public static int sizeof(long l){
  return LONG;
 }
 public static int sizeof(double d){
  return DOUBLE;
 }
 public static int sizeof(Object o){
  init(o);
  return sizeof0(o);
 }
 private static int sizeof0(Object o) {
  int size=OBJECT;
  //if the object is null
  if(o==null) return REFERENCE;
  
  Map map=(Map)objs.get();
  Class c=o.getClass();

  //if it is array
  if(c.isArray()){
   int[] dimension=getDimension(o);
   int len=dimension.length;
   
   
   
   Object obj=o;
   
   int num=1;
   for(int j=0;j<len-1;j++) num*=dimension[j];
   if(dimension[len-1]==0){
    size+=num*REFERENCE;
   }
   else{
    num*=dimension[len-1];
    //处理递归
    int[] index;
      
    Class type=c;
    while(type.isArray()) type=type.getComponentType(); 
    //基本类型的数组
    if(type.isPrimitive()){
     size+=num*sizeofPrimitive(type);
    }
    //引用类型数组
    else{
     
     for(int k=0;k<num;k++){
      index=countToIndex(k,dimension);
      Object temp=obj;
      for(int m=0;m<len;m++){
       temp=Array.get(temp,index[m]);
      }
      //加入数组中的所有对象
      
      
      if(!map.containsKey(temp)){
       size+=sizeof0(temp);
       map.put(temp,null);
      }      
     }
    }
   }
  }
  
  
  // all not-static fields
  Field[] fs=getFields(o.getClass());

  for(int i=0;i<fs.length;i++){
   
   Field f=fs[i];
   if(!Modifier.isStatic(f.getModifiers())){

    Class type=f.getType();
    //if it is primitive
    if(type.isPrimitive()){
     size+=sizeofPrimitive(type); 
    }
    //recurtive
    else{
     Object obj=null;
     try{
      obj=f.get(o);
     }
     catch(IllegalAccessException e){
      //won't be happen
      throw new RuntimeException("impossible");
     }
     if(!map.containsKey(obj)){
      size+=sizeof0(obj);
      map.put(obj,null);
     }
    }
   }
  }

  
  return size;
 }

 private static  int[] countToIndex(int count,int[] d){
  int[] res=new int[d.length];
  int c=count;
  int i=1;
  while(c>0){  
   int t=1;
   for(int j=i;j<d.length;j++) t*=d[j];
   if(t>c) i++;
   else{
    res[i-1]=c/t;
    c=c%t;
   }
  }
  return res;
 }

 private static int sizeofPrimitive(Class c){
  if (c==boolean.class){
   return BOOLEAN;
  }
  else if(c==byte.class){
   return BYTE;
  }
  else if(c==char.class){
   return CHAR;
  }
  else if(c==short.class){
   return SHORT;
  }
  else if(c==int.class){
   return INT;
  }
  else if(c==float.class){
   return FLOAT;
  }
  else if(c==long.class){
   return LONG;
  }
  else if(c==double.class){
   return DOUBLE;
  }
  else{
   throw new IllegalArgumentException("Thrown by sizeOfPrimitive()");
  }
 }
 private static int[] getDimension(Object obj){
  int dimension=0;
  Class c=obj.getClass();
  while(c.isArray()){
   dimension++;
   c=c.getComponentType();
  }
  int[] res=new int[dimension];
 
  Object o=obj;
  for(int i=0;i<dimension-1;i++){
   res[i]=Array.getLength(o);
   o=Array.get(o,0);
  }
  res[dimension-1]=Array.getLength(o);

  return res;
 }
 
 private static Field[] getFields(Class c){
  Class superClass=c.getSuperclass();
  Field[] s=null;
  if(superClass!=null){
   getFields(superClass);
  }
  Field[] fs=c.getDeclaredFields();
  
  //设置为可访问的
  Field.setAccessible(fs,true);
  

  //合并
  int size=0;
  if(s!=null) size+=s.length;
  if(fs!=null) size+=fs.length;

  Field[] result=new Field[size];
  int index=0;
  if((s!=null)&&(s.length>0)){
   System.arraycopy(s,0,result,0,s.length);
   index+=s.length;
  }
  if((fs!=null)&&(fs.length>0)){
   System.arraycopy(fs,0,result,index,fs.length);
  }

  return result;
 }
}

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