java 将侦听器与线程一起使用
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Using Listener with Threads
提问by Yannick Wald
Say I have an Object Foo that wants to get informed by several running instances of a Thread using a listener interface. E.g.
假设我有一个对象 Foo，它希望使用侦听器接口通过线程的多个正在运行的实例获取通知。例如
The interface:
界面：
public interface ThreadListener {
public void onNewData(String blabla);
}
The class Foo:
Foo 类：
public class Foo implements ThreadListener {
public Foo() {
FooThread th1 = new FooThread();
FooThread th2 = new FooThread();
...
th1.addListener(this);
th2.addListener(this);
...
th1.start();
th2.start();
...
}
@Override
public void onNewData(String blabla) {
...
}
}
The Thread:
主题：
public FooThread extends Thread {
private ThreadListener listener = null;
public void addListener(ThreadListener listener) {
this.listener = listener;
}
private void informListener() {
if (listener != null) {
listener.onNewData("Hello from " + this.getName());
}
}
@Override
public void run() {
super.run();
while(true) {
informListener();
}
}
}
In the worst case onNewData(..) is invoked by several threads at the same time. What will happen with Foo? Is it going to crash or not?
在最坏的情况下，onNewData(..) 被多个线程同时调用。Foo会发生什么？它会崩溃吗？
回答by assylias
- Your
Fooclass has no state (fields), so unless it uses external shared resources (e.g. files...) it is thread safe - Starting thread from a constructor is generally a bad idea although in the case of a state-less object, I suppose it is fine
- if
onNewDatadoes not access shared data it will work as expected, if it does, the outcome will depend on how the method is implemented.
- 您的
Foo类没有状态（字段），因此除非它使用外部共享资源（例如文件...），否则它是线程安全的 - 从构造函数启动线程通常是一个坏主意，尽管在无状态对象的情况下，我认为这很好
- 如果
onNewData不访问共享数据，它将按预期工作，如果访问，结果将取决于该方法的实现方式。
