Javadocs of CopyOnWriteArrayList says A thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array. I am confused now when will other threads see changes present in this fresh copy? Does this mean there will be number of copies of the underlying array equal to the number of mutations of the collection
CopyOnWriteArrayList Javadocs说 ArrayList的线程安全变体，其中所有可变操作（add，set等）都通过创建底层数组的新副本来实现。 现在我很困惑其他线程何时会看到这个新副本中存在的变化？ 这是否意味着底层数组的副本数量等于集合中的突变数量？ 如果不是，那么这些单独副本的更改何时传输到底层数组，以便其他线程可以看到它们？ 这里的想法是，无论何时添加或移除到CopyOnWriteArrayList ，基本数组都基本上与修改一
重写equals和hashCode时必须考虑哪些问题/陷阱？ The theory (for the language lawyers and the mathematically inclined): equals() (javadoc) must define an equivalence relation (it must be reflexive, symmetric, and transitive). In addition, it must be consistent (if the objects are not modified, then it must keep returning the same value). Furthermore, o.equals(null) must always return false. ha
重写equals和hashCode时必须考虑哪些问题/陷阱？ 理论（针对语言律师和数学倾向）： equals() （javadoc）必须定义一个等价关系（它必须是自反的，对称的和可传递的）。 另外，它必须一致（如果对象没有被修改，那么它必须保持返回相同的值）。 此外， o.equals(null)必须始终返回false。 hashCode() （javadoc）也必须是一致的（如果对象没有用equals()修改，它必须保持返回相同的值）。 这两种方法之间的关系是： 每
I was studying the legacy API's in the Java's Collection Framework and I learnt that classes such as Vector and HashTable have been superseded by ArrayList and HashMap . However still they are NOT deprecated, and deemed as legacy when essentially, deprecation is applied to software features that are superseded and should be avoided, so, I am not sure when is a API deemed legacy and when
我正在研究Java Collection Framework的遗留API，并且我了解到像Vector和HashTable这样的类已经被ArrayList和HashMap所取代。 但是，它们不会被弃用，并且在被弃用且应该避免的软件功能被应用时，将其视为遗留，因此，我不确定API什么时候被视为遗留以及何时弃用。 从官方的Sun词汇表： 弃用 ：指不再推荐的类，接口，构造函数，方法或字段，并可能在将来的版本中停止存在。 从何时开始弃用指南： 你可能听说过这个词
I am coding a method that return an instance of FragmentManager as shown in the code belwo. the prblem is, I want to throw an exception if the context passed to the method is null and then terminate the App. what happens is, when I pass null to the method mentioned below, the App closes but the message in the NullPointerException which is : getFragmentManagerInstance: Context reference is nul
我正在编写一个方法，返回一个FragmentManager实例，如代码示例所示。 问题是，如果传递给方法的上下文为空，然后终止应用程序，我想抛出异常。 会发生的是，当我将null传递给下面提到的方法时，应用程序关闭，但NullPointerException中的消息是： getFragmentManagerInstance: Context reference is null 不显示 请让我知道如何抛出异常并正确终止应用程序。 库 ： public static FragmentManager getFragmentManagerI
if (aDate.after(cottageHospital.getLastWardChangeDate(thePatient))) { Ward newWard = (Ward) changeWardNewWardList.getSelectedValue(); changeWardArea.setText("Patient " + thePatient + " moved to " + newWard + "ward."); cottageHospital.changeWard(thePatient, newWard, aDate); } I have an if statement that is part of a larger method, the statement com
if (aDate.after(cottageHospital.getLastWardChangeDate(thePatient))) { Ward newWard = (Ward) changeWardNewWardList.getSelectedValue(); changeWardArea.setText("Patient " + thePatient + " moved to " + newWard + "ward."); cottageHospital.changeWard(thePatient, newWard, aDate); } 我有一个if语句，它是更大方法的一部分，该语句将日期aDate与另一个日期值进
Background I would like to understand why a snippet of code does not throw a NullPointerException. Source Code Consider the following code: public class Agent { public List files = new ArrayList(); public void deliver() { if( files != null && files.iterator().hasNext() ) { File file = (File)files.iterator().next(); } files = new ArrayList(); } } The deliv
背景 我想知道为什么的代码片段不会抛出NullPointerException。 源代码 考虑下面的代码： public class Agent { public List files = new ArrayList(); public void deliver() { if( files != null && files.iterator().hasNext() ) { File file = (File)files.iterator().next(); } files = new ArrayList(); } } deliver方法被重复调用，而下面的代码在单独的线程中运行： public
When running this: public class WhatTheShoot { public static void main(String args[]){ try { throw null; } catch (Exception e){ System.out.println(e instanceof NullPointerException); System.out.println(e instanceof FileNotFoundException); } } } The response is: true false Which was fairly stunning for me. I would have tho
运行时： public class WhatTheShoot { public static void main(String args[]){ try { throw null; } catch (Exception e){ System.out.println(e instanceof NullPointerException); System.out.println(e instanceof FileNotFoundException); } } } 答复是： true false 这对我来说相当惊人。 我原以为这会造成编译时错误。 为什么我可以在J
This is one for the java purists I think. I recently had an issue with a method to perform a custom parsing of String values to a Boolean. A simple enough task, but for some reason the method below was throwing a NullPointerException in the null case... static Boolean parseBoolean(String s) { return ("1".equals(s) ? true : ("0".equals(s) ? false : null)); } The return type for the method
这是我认为的java纯粹主义者之一。 我最近有一个方法来执行String值的自定义分析到布尔值的问题。 一个足够简单的任务，但由于某种原因，下面的方法在null情况下抛出NullPointerException ... static Boolean parseBoolean(String s) { return ("1".equals(s) ? true : ("0".equals(s) ? false : null)); } 该方法的返回类型是布尔值，为什么会抛出NullPointerException？ 从调试开始，似乎在嵌套内联条件语句的计算结
I experienced slowness in HTMLUnit 2.12, and therefore disabled CSS as explained in HTMLUnit : super slow execution?. I want to understand what the trade-off is. Does it mean that I cannot use XPath selectors? Are there other tradeoffs? XPath selectors only take into account the html/xml document. CSS does not affect your queries. If it would then it would have non-deterministic results b
我在HTMLUnit 2.12中经历了缓慢，因此禁用CSS，如HTMLUnit中所述：超慢执行。 我想了解什么是权衡。 这是否意味着我无法使用XPath选择器？ 是否有其他折衷？ XPath选择器只考虑html / xml文档。 CSS不会影响您的查询。 如果它会根据应用的CSS规则得到非确定性结果。 就CSS选择器和XPath选择器而言，您可以安全地使用这些选项，而无需事先加载任何CSS。 加载它们将不会影响您将收到的结果。 对于CSS来说，对HTMLUnit
My timer looks like this: runnable = new Runnable() { @Override public void run() { while (running) { try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } handler.post(new Runnable() { @Override p
我的计时器看起来像这样： runnable = new Runnable() { @Override public void run() { while (running) { try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } handler.post(new Runnable() { @Override pu