I've Oracle Advanced Queue implemented & I'm writing a listener program. Below is my sample: package com.myprog; import java.io.File; import java.io.FileInputStream; import java.io.StringWriter; import java.sql.Connection; import java.sql.DriverManager; import java.util.Properties; import javax.jms.ExceptionListener; import javax.jms.JMSException; import javax.jms.Message; import
我已经实现了Oracle高级队列和我正在编写一个监听器程序。 以下是我的示例： package com.myprog; import java.io.File; import java.io.FileInputStream; import java.io.StringWriter; import java.sql.Connection; import java.sql.DriverManager; import java.util.Properties; import javax.jms.ExceptionListener; import javax.jms.JMSException; import javax.jms.Message; import javax.jms.MessageConsumer; import
I want create text file but if the file already exists it should not create new file but should append the text to the content (at the end) of the existing file. How can I do it in Java? for every one second I'm reading data from inputstream when i stop reading and again i start reading data at that time i should write to same file if file already exist does I have to check the condition
我想创建文本文件，但如果文件已经存在，它不应该创建新文件，而应该将文本附加到现有文件的内容（最后）。 我怎样才能在Java中做到这一点？ 对于每一秒钟，我正在从输入流读取数据，当我停止阅读时，再次开始阅读数据，那时我应该写入相同的文件，如果文件已经存在 我是否必须检查条件： if(file.exists){ } else{ new File(); } 我必须做什么？ 您可以使用以下代码追加到已存在的文件 - try { BufferedWrite
I am working on an application and one design approach involves extremely heavy use of the instanceof operator. While I know that OO design generally tries to avoid using instanceof , that is a different story and this question is purely related to performance. I was wondering if there is any performance impact? Is is just as fast as == ? For example, I have a base class with 10 subclasses.
我正在开发一个应用程序，一种设计方法涉及对instanceof操作符的极大使用。 虽然我知道面向对象设计通常试图避免使用instanceof ，但这是一个不同的故事，而这个问题纯粹与性能有关。 我想知道是否有任何性能影响？ 是和==一样快吗？ 例如，我有一个有10个子类的基类。 在接受基类的单个函数中，我会检查类是否是子类的实例并执行一些例程。 我想解决这个问题的其他方法之一就是使用“type id”整数基元，并使用位掩码来表
Now I'm writing an ORM Framework and very care about performance. In this Framework , I have to use instanceof and Class.isAssignableFrom to check type compability. So I have a little doubt about the performance of instanceof and Class.isAssignableFrom How slow exactly it is? How instanceof is implemented inside JAVA? The short answer is that it is platform dependent. The long ans
现在我正在编写一个ORM框架，并非常关心性能。 在这个框架中，我必须使用instanceof和Class.isAssignableFrom来检查类型的Class.isAssignableFrom 。 所以我对instanceof和Class.isAssignableFrom的性能有点怀疑 它究竟有多慢？ 如何在JAVA内部实现instanceof？ 简单的答案是它依赖于平台。 长时间的答案是，你应该能够通过编写一个使用instanceof的测试用例，在循环中运行它来确保它获得JIT编译，然后转储和检查本
This question already has an answer here: The performance impact of using instanceof in Java 23 answers It does generate some overhead, combined with the subsequent casting. With recent version of Java the overhead has decreased. But anyway that's microoptimization - ie you should not worry about it in the general case. The real argument against instanceof is that in many cases there
这个问题在这里已经有了答案： 在Java 23中使用instanceof的性能影响应答 它确实会产生一些开销，并与后续的投射相结合。 随着最近版本的Java的开销下降。 但无论如何，这是微型优化 - 即你在一般情况下不应该担心它。 反对instanceof的真实观点是，在许多情况下，有更好的面向对象方法来实现所需的行为。 如果编译器可以证明实例，它可能会或可能不会产生任何开销。 即使编译器不能立即证明目标，开销也很小。 几个
Trying to answer to this ticket : What is the difference between instanceof and Class.isAssignableFrom(...)? I made a performance test : class A{} class B extends A{} A b = new B(); void execute(){ boolean test = A.class.isAssignableFrom(b.getClass()); // boolean test = A.class.isInstance(b); // boolean test = b instanceof A; } @Test public void testPerf() { // Warmup the code for
试图回答这张票：instanceof和Class.isAssignableFrom（...）有什么区别？ 我做了一个性能测试： class A{} class B extends A{} A b = new B(); void execute(){ boolean test = A.class.isAssignableFrom(b.getClass()); // boolean test = A.class.isInstance(b); // boolean test = b instanceof A; } @Test public void testPerf() { // Warmup the code for (int i = 0; i < 100; ++i) execute();
I have a multithreaded Java code in which: several threads read stateful objects from the synchronized shared storage (ie as a result of this, some threads may reference the same objects); each thread then invokes a method process() and passes its object there; process() processes objects in some way, which may result changing the objects state; these state changes should be synchronized.
我有一个多线程的Java代码，其中： 几个线程从同步共享存储中读取有状态的对象（即由于这个原因，一些线程可能引用相同的对象）; 每个线程然后调用一个方法process()并在那里传递它的对象; process()以某种方式处理对象，这可能导致更改对象状态; 这些状态变化应该同步。 我已经创建了一个这样的方法： public void process(Foo[] foos) { for (final Foo foo : foos) { if (foo.needsProcessing()) {
In what cases is it necessary to synchronize access to instance members? I understand that access to static members of a class always needs to be synchronized- because they are shared across all object instances of the class. My question is when would I be incorrect if I do not synchronize instance members? for example if my class is public class MyClass { private int instanceVar = 0;
在什么情况下需要同步对实例成员的访问？ 我知道对类的静态成员的访问总是需要进行同步 - 因为它们是在类的所有对象实例之间共享的。 我的问题是如果我不同步实例成员，我什么时候会不正确？ 例如，如果我的课是 public class MyClass { private int instanceVar = 0; public setInstanceVar() { instanceVar++; } public getInstanceVar() { return instanceVar; } } 在
I am studying java threads and deadlocks, I understand deadlock's examples but I wonder if there are general rules to follow to prevent it. My question is if there are rules or tips that can be applied to the source code in java to prevent deadlocks? If yes, could you explain how to implement it? Some quick tips out of my head don't use multiple threads (like Swing does, for exampl
我正在研究Java线程和死锁，我理解死锁的例子，但我想知道是否有一些通用规则可以用来防止它。 我的问题是，如果有规则或技巧可以应用于java中的源代码来防止死锁？ 如果是的话，你能解释一下如何实现它吗？ 一些快速提示我的头脑 不要使用多个线程（比如像Swing一样，例如强制所有东西都在EDT中完成） 不要一次持有多个锁。 如果你这样做，总是以相同的顺序获取锁 在锁定时不要执行外部代码 使用可中断的锁 封
I have 2 matrices and I need to multiply them and then print the results of each cell. As soon as one cell is ready I need to print it, but for example I need to print the [0][0] cell before cell [2][0] even if the result of [2][0] is ready first. So I need to print it by order. So my idea is to make the printer thread wait until the multiplyThread notifies it that the correct cell is ready to
我有2个矩阵，我需要将它们相乘，然后打印每个单元格的结果。 只要一个单元准备好我需要打印，但是例如我需要打印[0] [0]细胞前细胞[2]即使的结果[2] [0]是准备第一[0] 。 所以我需要按顺序打印它。 所以我的想法是让打印机线程等待，直到multiplyThread通知它正确的单元已准备好打印，然后printerThread将打印单元并返回等待等等。 所以我有这个线程可以进行乘法运算： public void run() { int countNumOfActions =