在《Java Concurrency in Practice》中，对于发布对象和数据逸出有两种示例，
其中之一是：
Listing 3.6. Allowing Internal Mutable State to Escape. Don't Do this.
class UnsafeStates {
private String[] states = new String[] {
"AK", "AL" ...
};
public String[] getStates() { return states; }
}这个好理解；
另外一个示例是：
Listing 3.7. Implicitly Allowing the this Reference to Escape. Don't Do this.
public class ThisEscape {
public ThisEscape(EventSource source) {
source.registerListener(
new EventListener() {
public void onEvent(Event e) {
doSomething(e);
}
});
}
}作者认为“it implicitly publishes the enclosing ThisEscape instance as well, because inner class instances contain a hidden reference to the enclosing instance.”
作者的改进建议是：
If you are tempted to register an event listener or start a thread from a constructor, you can avoid the improper construction by using a private constructor and a public factory method, as shown in SafeListener in Listing 3.8.
Listing 3.8. Using a Factory Method to Prevent the this Reference from Escaping During Construction.
public class SafeListener {
private final EventListener listener;
private SafeListener() {
listener = new EventListener() {
public void onEvent(Event e) {
doSomething(e);
}
};
}
public static SafeListener newInstance(EventSource source) {
SafeListener safe = new SafeListener();
source.registerListener(safe.listener);
return safe;
}
}
作者对于错误的原因是这样解释的：
ThisEscape illustrates an important special case of escapewhen the this references escapes during construction. When the inner EventListener instance is published, so is the enclosing ThisEscape instance. But an object is in a predictable, consistent state only after its constructor returns, so publishing an object from within its constructor can publish an incompletely constructed object. This is true even if the publication is the last statement in the constructor. If the this reference escapes during construction, the object is considered not properly constructed.
有谁能把这个原因解释清楚点，即：为什么说这是一个未完成的对象呢，一旦内部匿名类那段代码执行完后，对象不就被注册了么？
