Java“同步”关键字不禁止其他线程更改类成员的内部元素
我指的是JCP 4.4.2，它具有以下示例代码，
@ThreadSafe
public class ImprovedList<T> implements List<T>{
private final List<T> list;
public ImprovedList(List<T> list){this.list=list;}
public synchronized boolean putIfAbsent(T x){
boolean contains = list.contains(x);
if(contains){
list.add(x);
}
return !contains;
}
@Override
public synchronized void clear(){list.clear();}
}
该书说此改进清单是安全的，但是我有一个问题：
构造函数“列表”的输入参数来自外部。因此，尽管putifabsent（）是 on rivevedlist上的同步，但不能保证将锁定锁定在ReverVeList的内部元素上。列表。如果另一个线程将任何类型[t]元素更改/添加到此list，rivevevabsent.putifabsent可能会导致未确定的状态。
请帮助纠正我的理解。
I'm referring to JCP 4.4.2 and it has following sample code
@ThreadSafe
public class ImprovedList<T> implements List<T>{
private final List<T> list;
public ImprovedList(List<T> list){this.list=list;}
public synchronized boolean putIfAbsent(T x){
boolean contains = list.contains(x);
if(contains){
list.add(x);
}
return !contains;
}
@Override
public synchronized void clear(){list.clear();}
}
The book said this ImprovedList is thread safe, but I have a question:
The input parameter of the constructor "list" is from outside. So, although putIfAbsent() is synchronized on ImprovedList, there is no guarantee the lock is put on the internal elements of ImprovedList.list. If another thread is changing/adding any type [T] element into this list, ImprovedList.putIfAbsent could result undetermined state, I guess.
Please kindly help to correct my understandings.
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是的，但是如果您看书，他们采取了这个假设：
此假设通过改进清单，代码为线程安全。
Yes exactly, but if you look in the book, they took this assumption:
Based on this assumption the code is thread-safe.