集合和集合是一样的吗？(Collection and Set are the same?)

 那么，这是一个常见的误解，java程序本质上是单线程的，因为它们不是。 当你启动一个Java程序时，它将在一个Java虚拟机内执行，它启动其他几个线程来执行你的代码。 检查这个漂亮的博客： 
 
 http://blog.jamesdbloom.com/JVMInternals.html#jvm_system_threads 
 
 在你的情况下，你最重要的是，你启动一个主线程，执行主方法。 从那里你启动两个独立的线程Thread1和Thread2，这两个线程正在计划执行，但你不知道什么时候OS调度程序会被实际执行。 这是不确定的，原因很多： 
 
 
 
 您不知道调度程序使用什么算法来拾取要执行的线程， 
 
 
 你不知道你的处理器有多少核心，你的线程可能并行或串行运行 
 
 
 即时编译器可能会重新排列和优化您的代码， 
 
 
 CPU可能会重新安排读取和写入IO以优化代码的执行， 
 
 
 您的代码中可能存在导致数据竞争，竞争状况，饥饿等的错误。 
 
 
 Java并发性是一个很难的话题，我发给你的博客条目是一个很好的开始，随它去吧。 对于严肃的阅读去这里http://www.amazon.com/Java-Concurrency-Practice-Brian-Goetz/dp/0321349601 。 
 
 祝你好运。 

Well, this is a common misconception, that java programs are single threaded by nature, because they are not. When you start a java program it's being executed inside a Java Virtual Machine, which starts several other threads to execute your code. Check this nice blog:
 
http://blog.jamesdbloom.com/JVMInternals.html#jvm_system_threads
 
In your case you most important is, that you start a main thread, which executes a main method. From there you start two separate threads Thread1 and Thread2, which are being scheduled to be executed, but you don't know when they will be picked up by the OS scheduler to be actually executed. It's not deterministic for many reasons:
 
 
 
you don't know what algorithm scheduler is using to pick up threads to be executed,
 
 
you don't know how many cores your processors have, your threads might run in parallel or serially
 
 
Just In Time compiler might rearrange and optimise your code,
 
 
CPU might rearrange reads and writes to IO to optimise the execution of your code,
 
 
you might have bugs in your code that lead to data races, race conditions, starvations etc. 
 
 
Java concurrency is a hard topic and the blog entry that I've sent you is a good place to start, go with it. For serious reading go here http://www.amazon.com/Java-Concurrency-Practice-Brian-Goetz/dp/0321349601.
 
Good luck.