作者zheng2010 (自我催眠)
看板java
標題[問題] 物件與多執行緒的問題
時間Sat May 18 00:13:32 2013
各位前輩們好，
在下面那簡單的程式碼中
s會重複被assign，所以
我預期的輸出結果是
s1=this is obj1
s2=this is obj2
s2=this is obj2 <--- Main can Access
s2=this is obj2 <--- Main can Access
s2=this is obj2 <--- Main can Access
s2=this is obj2 <--- Main can Access
s2=this is obj2 <--- Main can Access
s2=this is obj2 <--- Main can Access
但是因為字串是由thread來印的
所以實際上的輸出如下
s1=this is obj1
s2=this is obj2
s1=this is obj1
s2=this is obj2 <--- Main can Access
s1=this is obj1
s2=this is obj2 <--- Main can Access
s1=this is obj1
s2=this is obj2 <--- Main can Access
s1=this is obj1
s2=this is obj2 <--- Main can Access
也就是說第一個物件還是存在著?
照理說不是進行第二次的s = new CAR("s2=this is obj2")後
GC就會去把access不到的記憶體清掉嗎，那為什麼還是會一直印出s1=.....
還是說是因為thread的關係?(thread 負責印出字串)
謝謝
---------------程式碼-----------------------------
public class Game{
static CAR s;
public static void main(String []args){
s = new CAR("s1=this is obj1");
s = new CAR("s2=this is obj2");
try{
Thread.sleep(2000);
}catch(Exception e)
{
}
s.x+=" <--- Main can Access";
}
}
class CAR {
CAR(String s)
{
x=s;
Thread thread1 = new Thread(aa);
thread1.start();
}
public String x;
private Runnable aa= new Runnable(){
@Override
public void run() {
while(true)
{
System.out.println(x);
try{
Thread.sleep(1000);
}catch(Exception e)
{
}
}
}//run
};
}
--
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1F：推 PsMonkey:只是 s 沒有指向第一個 car，不代表第一個 car 沒人 ref 05/18 00:21
2F：推 Elohim123:乍看起來是因為每次在做new CAR()時constructor裡面 05/18 00:22
3F：→ Elohim123:都會去做thread1.start()這樣 ? 05/18 00:23
4F：→ zheng2010:可是thread1也是物件的一部分，所以物件自己ref自己? 05/18 00:30
5F：→ asilzheng:沒說過 GC 會馬上動作吧? 05/18 00:37
6F：推 PsMonkey:看一下 Thread.init() 吧 05/18 00:42
7F：→ zheng2010:回a大 如果第一個car還有人ref GC應該就不會清掉它吧? 05/18 00:56
8F：→ cha122977:還有人ref阿 不然怎麼印出來的? 05/18 04:50