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  Why accessing Java HashMap may cause infinite loop in concurrent environment

HashMap in Java is frequently used to handle key/value pairs. But it is not a good candidate to be used in concurrent environment where ConcurrentHashMap should be used instead. If used in concurrent environment, it may cause lots of unexpected behavior even including make the program getting into an infinite loop situation. To understand how this can happen, let's first discuss how HaspMap works internally. In this post we will use implementation of HashMap before Java 8 as example, Java 8 prov...

   JAVA,HASHMAP,INFINITE LOOP     2020-03-29 01:47:00

  Generate certificate in Java -- Self signed certificate

This is the first post in this series which I will show you how to generate SSL certificate in Java programmatically. Certificates are frequently used in SSL communication which requires the authentication of server to client. This is to make the client to trust that the server is actually the one it claims. Certificates are really important on the Internet. All HTTPS communications on the Internet need the server side to present their certificates signed by trusted CAs. The basic flow of a requ...

   Java,Certificate,X509     2014-07-30 07:42:18

  JavaScript's New Features: Exploring the Latest Additions to the Language

As the web continues to evolve, so too does the JavaScript ecosystem. With the release of ECMAScript 2023 (ES2023), JavaScript developers can now leverage a range of new features that promise to improve code quality, readability, and maintainability. In this blog post, we'll dive into some of ES2023's most exciting additions and provide practical examples of how they can be used in your projects. 1. Private Fields and Methods in Classes One of the most anticipated features in ES2023 is the intro...

   JAVASCRIPT,ES2023     2023-04-16 01:41:58

  Access control in Java -- Permission check order

Previously we showed you how to turn on SecurityManager in Java. After SecurityManager is turned on, a series of permission checks will be applied on the code you are calling in your application to protect some resources against malicious access such as files, sockets etc. To perform these permission checks, a set of Permissions will be created and checked using the AccessController. The AccessController has three purposes : To decide whether an access to a critical system resource is to be all...

   JAVA,SECURITY,ACCESSCONTROLLER     2016-03-07 04:17:40

  Remote execute command in Java example

Frequently there is a need to logon to a remote system and run some commands or programs to get the output, many software can serve this purpose such as putty and gitshell.These software usually provide secure access to the remote system. But have you ever wondered what to do if you need to run commands on many different systems at the same time and get all these results back at a single place? Especially in big data era, many tasks may run on different distributed systems and you want o have a ...

   JSch, Example, Distributed system, SSH2     2014-12-12 03:20:19

  Use DTrace to diagnose gdb issues

A few days ago, I installed the newest 64-bit gdb program (version 7.7.1) on Solaris 10 (X86_64 platform) to debug programs. After playing with the gdb a day, I found 2 issues about gdb:(1) The "set follow-fork-mode child" command doesn't take effect. By default, after the parent process forks the child process, the gdb will track the parent process, so this command can make gdb begin to follow the child process. But this command works OK on Linux.(2) The gdb can't parse the 32-bit application c...

   DTrace, debug, gdb, UNIX     2014-06-28 05:11:20

  try { return } finally {}

Do you know what value will be printed when following program is ran? class Test { public int aaa() { int x = 1; try { return ++x; } catch (Exception e) { } finally { ++x; } return x; } public static void main(String[] args) { Test t = new Test(); int y = t.aaa(); System.out.println(y); } } And before answering the above question, do you have answers to following questions? If ther...

   JAVA,JAVA INTERVIEW QUESTION     2016-09-26 08:06:28

  What does super.clone() do?

Object class has a protected clone() method declared to make it possible for all classes make a clone of itself when needed. The clone() is often used when a new instance of the class is needed while at the same time to maintain the same state as the original object. Any class which wants to have clone enabled has to implement the marker interface Cloneable. If a class which implements Cloneable doesn't override the Object.clone() method, the Object.clone() method will be called to just make a b...

   Cloneable,super.clone(),clone,Java     2015-01-07 05:25:52

  Use Memory Analyzer Tool in Eclipse

When developing applications, we often encounter memory issues of an application. To analyze how much memory each class takes, we need to have some specific tools to assist us. One of them is Memory Analyzer Tool on Eclipse. The Eclipse Memory Analyzer is a fast and feature-rich Java heap analyzer that helps you find memory leaks and reduce memory consumption. To use the Memory Analyzer Tool, you first need to install it on Eclipse. You can go to Help -> Install New Software.... Paste  h...

   Memory analyzer tool, Eclipse,heap dump, HPROF     2014-10-28 07:22:35

  Java AbstractMethodError explained and demonstrated

According to Oracle Java API documentation, AbstractMethodError is a kind of runtime error where the application is having some incompatible changes which leads to a missing implementation of an abstract method. Below is the official description. Thrown when an application tries to call an abstract method. Normally, this error is caught by the compiler; this error can only occur at run time if the definition of some class has incompatibly changed since the currently executing method was last co...

   JAVA,ABSTRACTMETHODERROR     2016-07-22 22:03:20

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