Programmer's Notebook

This is my learning notes about the SQL (based on  MySql ). As far as I known, Mysql was acquired by Oracle , whose mainly product is also the enterprise highly professional database, and the founder of the Mysql worried the future of the MySQL, then he started another open sourced database named MariaDB . I consider the Mysql and MariaDB the same thing, they even have the same command line tool name. And with no hesitate, I use MariaDB as the alternative to Mysql in the tutorial. Database Creation The operation of Database include Change, Create, Alter, Drop database. USE db_name ; CREATE DATABASE IF NOT EXIST db_name CHARACTER SET = utf - 8 ; ALTER DATABASE db_name CHARACTER SET = utf - 8 ; DROP DATABASE IF EXIST db_name ; Table Creation The basic composition of a database is its tables, table schema definition is the beginning stage in the database design. There is two import aspect in define a table schema, the column data types and the constric...

Memory in JVM One of the benefits of JVM is the isolation of memory from the host OS, so that if there are some errors in the JVM, the influence is only limited to current JVM process. Actually, the memory in a JVM can be separated to many functional parts, for the simplicity, Heap, and Stack. The Heap is this article's target, Out of Memory Error When the Heap size running to its limitation, the out of Memory Error throws, and the process will crash. It is really easy to repeat this Error, and just write codes to allocate memory repeatedly. while (true) { byte [ ] twn = new byte [ ( int ) ( 1024 L * 1024 L * 20 ) ] ; mLists . add ( twn ) ; } If you write some cache or Memory management app, then it is really the critic part to manage the memory. There are many reasons to trigger this error, serious memory leak or memory limitation, so how to enlarge the memory limitation. java -Xmx:1024m -Xms:512m This is the common way for  a general java command l...

The multi-threading synchronization questions always concentrate on a few keywords: wait, notify, notifyAll, synchronized, volatile. The following question is the hardest, I ever met. The thread t1 should print integer number from 1–52, the thread t2 should print character from A-Z, the question is how to let the final result to be 12A34B56C… by implement Printer class. (The Printer class is already finished by the way) public class Main { public static void main ( String [ ] args ) { System . out . println ( "Hello World!" ) ; Printer p = new Printer ( ) ; Thread t1 = new NumberPrinter ( p ) ; Thread t2 = new LetterPrinter ( p ) ; t1 . start ( ) ; t2 . start ( ) ; } } public class LetterPrinter extends Thread { private Printer p ; public LetterPrinter ( Printer p ) { this . p = p ; } public void run ( ) { for ( char c = 'A' ; c < = ...

In this post, I tried to wrote some Job interview questions, that I met during my Job interview journey. Yeah, some of the them are still so fresh, because I mess up them a lot. However, A sketch notebook is always better than a good memory, especially in the situation of the lack practice exercise. finalize function The finalize method is used in JVM’s GC collection. But, it was said that it never guaranteed to be called during the collection, that’s means unpredictable, so I guess why I should put the resource release code into an unpredictable method, still be puzzled. How to write a singleton and thread-safe class? Following is an ordinary Singleton class without thread-safe features. public class Singular { private static Singular sInstance ; private Singular ( ) { } public static Singular getInstance ( ) { if ( sInstance = = null ) { sInstance = new Singular ( ) ; } return sInstance ; ...

ReactiveX Operations Table of Contents Resources ReactiveX Operations Sample Source code 1 Resources http://reactivex.io/documentation/operators.html http://reactivex.io/tutorials.html https://github.com/ReactiveX/RxJava/wiki/Additional-Reading 2 ReactiveX Operations To understand ReactiveX, We must consider everything as a stream, after that, the operations of ReactiveX stream was so complicated, that we can trade them as a new language, which operates the stream. The ReactiveX's Official document classify its operations as following categories: Creating Observables Transforming Observables Filtering Observables Combining Observables Error Handling Operations Observable Utility Operators Conditional and Boolean Operators Mathematical and Aggregate Operators BackPressure Operators Connectable Observable Operators Operators to Convert Observables Beside above categories, ReactiveX also provides the strategy to practice those operation...

ReactiveX Asynchronous Programming In Java There is a much detailed blog about ReactiveX of myself, checkout here . Table of Contents What is Asynchronous programming? Ways of Asynchronous programming in java Java Callback functions Java Future Benefit of RxJava 1 What is Asynchronous programming? The asynchronous issue exists, because of the blocking nature of every activity in reality. Every operation consume time, in theory, computers need to take at least one frequency to execute one instruct, it takes time between every oral conversation in the speed of voice at least. That's the blocking nature of this world, and the most valuable resource of all is the time. Some times the computer cannot wait for that longer for the blocking API, like in network communication, it waste of the computer resource so much. The another reason is the event-based scenario. In a network connected chatting app, program listens for every coming data continuously and output ...

How to install and switch between multi JDK? Table of Contents How to install and switch between multi JDK? Linux Mac OS X Common incompatible errors between different version 1 How to install and switch between multi JDK? I suppose that you are installed both java 7 and 8 into your system. So how to switch between them. 1.1 Linux # !/bin/ bash # java1.7.sh # source java1.7.sh to switch jdk 1.7 export JAVA_HOME = "/opt/tools/jdk1.7.0_60" export CLASSPATH =.:${ JAVA_HOME }/lib:${ CLASSPATH } export JDK_HOME = "/opt/tools/jdk1.7.0_60" export PATH = "/opt/tools/jdk1.7.0_60/bin" :${ PATH } # !/bin/ bash # source java1.8.sh to switch to JDK 1.8 export JAVA_HOME = "/opt/tools/jdk1.8.0_05" export CLASSPATH =.:${ JAVA_HOME }/lib:${ CLASSPATH } export JDK_HOME = "/opt/tools/jdk1.8.0_05" export PATH = "/opt/tools/jdk1.8.0_05/bin" :${ PATH } 1.2 Mac OS X # ~/.bash_profile ...

Dig into Https client connection in Android Table of Contents reference resources Java Keytool Certificate formats Use Https in Android Client Java SSLContext Two ways SSL verification TLSDemo 1 reference resources http://developer.android.com/training/articles/security-ssl.html http://ogrelab.ikratko.com/using-android-volley-with-self-signed-certificate/ http://stackoverflow.com/questions/2138940/import-pem-into-java-key-store http://stackoverflow.com/questions/3685548/java-keytool-easy-way-to-add-server-cert-from-url-port 2 Java Keytool Java keystore is like a database which store certificates and private keys and protect them by a password maybe. There are at least three format s of that, JKS, PKCS12, JCEKS, and many more. But in this tutorial, I only consider two formats of that JKS which is the Java's default format and BKS which is the Android's default format. How to import a certificate to the BKS style KeyStore? First step was to pr...