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  Hexadecimal and long in Java


Today I encountered a hexadecimal operation problem when I was implementing a bit reverse function for integer type. Basically in the implementation, there is an operation which is to do the bit operation & between one long integer and a hexadecimal number 0x00000000FFFFFFFFF. I was expecting that the high 32 bits of the long integer will be zeroed. But unfortunately I didn't get the expected result. The basic implementation is: long num=0x00F0_0000; num = (num>>16) | (num<<16); ...

   Hexadecimal,long,Java,bitwise operation     2014-06-18 23:44:32


  A boolean value interview question


Someone asked a question on StackOverflow, he was asked an interview question. The question is : Given 3 boolean variables a, b, c, return true if at least 2 out of the 3 are true. He gave the solution as follows :boolean atLeastTwo(boolean a, boolean b, boolean c) {    if ((a && b) || (b && c) || (a && c)) {        return true;    } else {        ret...

   bool,return,expression,conditional     2012-04-30 08:49:32


  Solution to getKeyCode() returns 0 in Java


The getKeyChar method always returns a valid Unicode character or CHAR_UNDEFINED. Character input is reported by KEY_TYPED events: KEY_PRESSED and KEY_RELEASED events are not necessarily associated with character input. Therefore, the result of the getKeyChar method is guaranteed to be meaningful only for KEY_TYPED events.For key pressed and key released events, the getKeyCode method returns the event's keyCode. For key typed events, the getKeyCode method always returns VK_UNDEFINED....

   Java,KeyCode,0,KeyListener     2011-06-06 10:38:11


  The several flavors of random in Java


Random number generation is one of most basic features in any programming language. The basic utilization is always the same: generate a random number between 0 and 1. With such a simple resource at hand we sometimes overlook some interesting features. What do we learn from the books? The most obvious and maybe intuitive way to generate random numbers in Java is simply calling: java.lang.Math.random() Random generation is in the Math utility class with abs, pow, floor...

   Java,Random,Thread,Math,Type     2012-03-22 14:17:44


  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


  Using Java keytool programmatically


Java provides a command line tool to access and operate different keystore which store keys and certificates. This tool is named keytool and is located at \bin.  On command line, you can issue below command to generate a keystore named mytest.jks which contains a private key and certificate chain. keytool -genkeypair -alias mykey -keyalg RSA -sigalg SHA256withRSA -dname CN=Java -storetype JKS -keypass password -keystore mytest.jks -storepass password Sometimes, in testing purpose, w...

   JAVA,KEYTOOL     2016-01-09 06:28:07


  JavaScript JVM runs Java


The world of software is made slightly crazy because of the huge flexibility within any computer language. Once you have absorbed the idea of a compiler written in the language it compiles what else is there left to gawp at? But... a Java Virtual Machine JVM written in JavaScript seems like another level of insanity.In fact it is a quite reasonable idea which is only made mad by the usual positions that Java, the top dog, and JavaScript the underling, usually occupy. Java is compiled not to mach...

   JavaScript,JVM,BicaVM,Cross platform,JavaScript written JVM     2011-11-22 02:51:38


  Multithreading interview questions in Java


Multithreading as a widespread programming and execution model allows multiple threads to exist within the context of a single process. These threads share the process' resources but are able to execute independently. The threaded programming model provides developers with a useful abstraction of concurrent execution. However, perhaps the most interesting application of the technology is when it is applied to a single process to enable parallel execution on a multiprocessor system.Many programme...

   Multithreading,Java,Interview     2012-05-28 06:33:25


  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


  Browse OpenJDK Java source code in Eclipse


Java 8 was recently released, many developers are now trying to extract the source code of Java 8 to find out how the new added features such as Lambda expressions, default method in interfaces, new Time API are implemented. How do you manage to download and browse the source code? Today we are going to show how to extract OpenJDK Java source code to Eclipse. Since OpenJDK is adopting Mercurial as its distributed version control system, you need to install Mercurial on your computer first before...

   OpenJDK,Java 8,Source code,Eclipse     2014-06-16 00:53:34