可以帮我解释一下程序的答案是怎么得来的吗？谢谢！

Question

class ValHold{
  public int i=10;
}public class Obparm{
public static void main(String[] args){
Obparm o =new Obparm();
o.amethod();
  }
        public void amethod (){                         
  int i=99; 
  int b= 0;                                                             
  ValHold v =new ValHold();
  System.out.println(v.i);//10
  System.out.println(i); //99                                         
  v.i=30; 
  b=v.i;                                                          
  another(v,b);                                                    
  System.out.println(v.i);                                            
}//End of amethod 
                                                           
public void another(ValHold v,int i){                                        
  i=0;                                                                  
  v.i=20;                                                            
  ValHold vh =new ValHold();                                               
  v = vh;                                                                  
  System.out.println(v.i);                                                                                                                     
}//End of another
                                                                         
}    
/*正确答案：
10
99
10  
20
请问为什么不是
10
99
10
30  
*/         

Answer 1

public void another(ValHold v,int i){                                        
      i=0;                                                                  
      v.i=20;                                                            
      ValHold vh =new ValHold();                                               
      v = vh;                                                                  
      System.out.println(v.i);                                                                                                                   }
another函数中的v首先指向主函数中的V，然后v.i被改为20，最后another函数中的v又指向vh，此时主函数中的v.i已经被改为了20
  

Answer 2

对象之间的传值和传引用问题。
好好理解下，理解透了就理解了传值和传引用了
本人觉得java中都是传值，不存在传引用，那样会更好理解一些东西

Answer 3

当最后一步时
public void another(ValHold v,int i)
{                                        
      i=0;                                                                  
      v.i=20;                                                            
      ValHold vh =new ValHold();                                               
      v = vh;                                                                  
      System.out.println（v.i);                                                                                                                     
    }
v.i已经是20了，没有改变，所以最后打印出的是20
这只是考查了一个引用关系

Answer 4

仍然是参数传递的问题
 public void another(ValHold v,int i){                                        
      i=0;                                                                  
      v.i=20; 
//到此时，这里的v与amethod中的v指向同一个对象，因此v.i = 20改变了该对象的i，也就是说amethod中的v.i已经变为20，而不是30了。                                                           
      ValHold vh =new ValHold();                                               
      v = vh;                                                                  
//现在，v与amethod中的v指向了不同的ValHold对象，这里的v.i = 10, 而amethod中的v.i仍为20  System.out.println(v.i);                                                                                                                     
    }//End of another所以打印出的自然就是
10
90
10
20