Java程式中遇到的問題

今天遇到一個問題，暫時想不通，趁熱先記下

package com.practise.test;
import java.util.Map;
import java.util.HashMap;

public class ATestOfClassAndMap 
{
    static A TestFunction (A a)
    {
        A resA = new A(a);
        resA.av++;
        resA.b.bv++;
        return resA;
    }
    public static void main(String[] args)
    {
        A a = new A();
        Map<String, B> testMap = new HashMap<String, B>();
        
        for(int i = 0; i < 10; i++)
        {
            a.setValue(TestFunction(a));
            testMap.put(String.format("%03d", i), a.b);
            System.out.println(String.format("%03d", i) + ":" + a.b.bv);
        }
        System.out.println("-----------------------------------------");
        for(String strI:testMap.keySet())
        {
            System.out.println(strI + ":" + testMap.get(strI).bv);
        }
    }

}
class A 
{
    int av;
    B b;
    public A() 
    {
        av = 0;
        b = new B();
    }

    public A(A ta) 
    {
        this.av = ta.av;
        this.b = new B(ta.b);
    }
    
    public void setValue(A ta)
    {
        this.av = ta.av;
        this.b.setValue(ta.b);;
    }
}

class B 
{
    int bv;
    public B() 
    {
        bv = 100;
    }
    
    public B(B tb) 
    {
        this.bv = tb.bv;
    }
    
    public void setValue(B tb)
    {
        this.bv = tb.bv;
    }
}

//輸出結果如下
--------------------------------------

000:101
001:102
002:103
003:104
004:105
005:106
006:107
007:108
008:109
009:110
-----------------------------------------
000:110
001:110
002:110
003:110
004:110
005:110
006:110
007:110
008:110
009:110