“StringBuffer 是同步的（或线程安全的），而 StringBuilder 不是”，为什么这会使 StringBuffer 方法变慢？
读完这篇文章后 - 'synchronized' 是什么意思？ 我仍然无法理解为什么 StringBuffer 会在线程安全环境中比 StringBuilder 慢。 StringBuffer 必须做哪些额外的耗时工作才使其变慢？
After reading this - What does 'synchronized' mean? I was still unable to understand why StringBuffer would be slower than StringBuilder in a thread-safe environment. What extra time-consuming work does StringBuffer have to do that makes it slower?
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即使获取和释放无竞争的锁，也会有一些小的开销，并且锁省略即使大多数实例不跨线程使用，它也不会在
StringBuffer中工作，因为实例可以跨线程使用。请参阅http://book.javanb.com/java-threads-3rd /jthreads3-CHP-5-SECT-1.html 了解 VM 在获取和释放锁时必须执行的操作的描述。
There is some small overhead acquiring and releasing even an uncontended lock, and lock elision won't work in
StringBuffereven if most instances are not used cross-thread because an instance could be.See http://book.javanb.com/java-threads-3rd/jthreads3-CHP-5-SECT-1.html for a description of what the VM has to do when acquiring and releasing locks.
确保一切同步运行。或者，更重要的是，不同步。同步方法调用意味着该方法的两次不同调用（如果该对象不是静态的，则在该对象上）必须轮流进入该方法。在线程 A（已在该方法中）完成之前，线程 B 无法进入方法synchMeth。
检查同步块是否已被锁定以及由谁锁定需要额外的时间。
Making sure things are running in synch. Or, more to the point, out of synch. Synchronizing a method call means two different invocations of that method (on that object if it is not static) have to take turns entering the method. Thread B cannot enter method synchMeth until Thread A (already in the method) has finished.
The checks for whether a synchronized block has been locked or not, and by whom, take extra time.
从 JavaDoc 阅读此内容
您必须阅读这篇文章 StringBuffer 与 StringBuilder 性能比较< /a>
其他有用的链接：StringBuffer 和 StringBuilder 类之间的区别。
Read this from JavaDoc
You must read this article on StringBuffer vs. StringBuilder performance comparison
Additional Useful Link : Difference between StringBuffer and StringBuilder class.