Lock.tryLock（）的用例(Use case for Lock.tryLock())

 在方法tryLock()的Lock接口的API文档中，粘贴了此代码示例， 
 
 
 
 此方法的典型用法习惯是： 
 
 
  Lock lock = ...;
  if (lock.tryLock()) {
      try {
          // manipulate protected state
      } finally {
          lock.unlock();
      }
  } else {
      // perform alternative actions
  }
 
 
 我的问题是，这个用例在Java 5之前是不存在的还是人们通过其他技术来实现它？ 
 
 我无法理解是否需要根据锁定可用性执行替代操作 。 
 
 有人可以为此解释实际用例吗？ 
 
 我确信这种技术不是直接替代synchronized写无死锁代码。 

At API docs of Lockinterface for method tryLock(), this code sample is pasted, 
 
 
 
A typical usage idiom for this method would be:
 
 
  Lock lock = ...;
  if (lock.tryLock()) {
      try {
          // manipulate protected state
      } finally {
          lock.unlock();
      }
  } else {
      // perform alternative actions
  }
 
 
My question is , does this use case not existed before Java 5 or folks used to implement it via some other techniques? 
 
I am not able to comprehend the need to execute perform alternative actions based on lock availability. 
 
Can somebody please explain real use cases for this?
 
I am sure this technique is not a straight forward replacement of synchronizedto write deadlock free code. 

原文：https://stackoverflow.com/questions/41788074