Java Insightz

In Software world, every project/product release has one version number associated with it to identify on which version of code base it has. Usually every project/product release has its version as follows. (Major).(Minor).(Maintenance/Enhancements).(Build Number) Major - If the release has Major changes in Project/Product then we need to increment this number by 1 Minor -   If the release has Minor changes in Project/Product then we need to increment this number by 1 Maintenance - If the release has Bug fixes or Small Enhancements then we need to increase this number by 1. Build Number :  Every time when we deliver build (latest code) to the QA to test, then we need to increase by 1. Partial Builds: If only some of the modules in the project modified and if those modules only delivered to QA means, it is called as partial builds. And this will be noted as build number along with alphabets. E.G of Build Numbers. Current Version of Project is 4.0.0.0 (4 Major ...

To know the IP address ----------- hostname -i (ip addres) hostname -s (short name) hostname -d (domain name) hostname -v (host name with domain name) To know the port number and running processes netstat -ano | findstr 80 If the file is huge in size and to see the file content we can use less <file name> e.g. less service.log Searching  matching pattern in file grep '<matching text>' <file name> e.g. grep 'Exception' service.log To grep the text from .gz files gzgrep '<matching text>' <gz file name> e.g. gzgrep 'Exception' service.log.gz ps -eaf | grep java ps aus | grep java tail -f <file Name> (auto updated last few lines) tail -100 logfile.log  (last 100 lines) ls -a  (hidden files) ls -lrt (Sort the files by time stamp) kill -9 <Process ID>   (get Process ID using ps -eaf | grep <process name>) e.g. kill -9 30102

Both ClassNotFoundException and NoClassDefFoundError errors will be occurred  when the required Class not present in the Class path.     ClassNotFoundException     ClassNotFoundException is an Exception got arized when trying load class using forName() method in class Class. findSystemClass method in class ClassLoader . loadClass method in class ClassLoader. e.g. Class.forName("oracle.jdbc.driver.OracleDriver") if the OracleDriver class file is not present in the Class path, then we will end up with this ClassNotFounException NoClassDefFoundError NoClassDefFoundError is an Error thrown at Runtime, when the Class is present during the compile time and not present during Runtime of the Code, then we will end up with this NoClassDefFoundError. 1. When required Class is not available at Runtime available only in compile time. 2.Since NoClassDefFoundError error is an Subclass of LinkageError, it will occur when one of the     Dependent ...

Extracting XML node value from CLOB  column in data base. Syntax ExtractValue(xml_fragment, xpath_expression) Query Syntax Select Extractvalue(XMLtype('<column name>'),'<XML node path>') From <table list> Where <conditions> Example Select Extractvalue(Xmltype(emp_xml), '/employees/empployee/emp_number') From employee  where  Status='A'; Updating a XML node value from CLOB  column in data base. Syntax UpdateXML(xml_target, xpath_expr, new_xml) Query Syntax Update table_name Set column_name=Updatexml(Xmltype('<column name>'),'<XML node path>','<Replacing XMLvalue'>).getclobval From <table list> Where <conditions>; Example Initial value /employees/empployee/emp_name/text() = Bhargava Update employe Set emp_name = Updatexml(Xmltype(emp_xml), '/employees/empployee/emp_name/text()','Bhargava Surimenu') where  emp_no=1207;

Comparable Interface Comparable is an interface in java, which has only comparTo (Object Obj) method in it. This is used to sort the user defined objects on specific member field. When Comparable is preferred. 1. Having provision of modifying the User defined object to implement the Comparable interface. (Third party jar class objects doesn't have provision to modify). 2. Have a requirement to sort the User defined object by one Member field in their natural sorting order. 3. Comparable provides only one Sorting for an Object. Our String and Wrapper Classes like Integer, Double, Long, BigDecimal etc. are override this compareTo method by implementing the Comparable Interface. For example, To sort the Bank Accounts  based on the amount it contains. 1. Create Account pojo with all the member fields including amount. 2. Implement the Account pojo with Comparable interface. 3. Override the compareTo(Object obj) method from Comparable interface. (Refer following cod...

Immutability. A Java object is considered to be immutable when its state (properties and contents) cannot change after it is created. Use of immutable objects is widely accepted as a sound strategy for creating simple, reliable code. Immutable objects are particularly useful in concurrent applications. Since they cannot change state, they cannot be corrupted by thread interference or observed in an inconsistent state. java.lang.String and java.lang.Integer classes are the Examples of immutable Immutable objects are simple to use test and construct. Immutable objects are thread-safe by default. Immutable objects are good Map keys and Set elements (Since state of these objects must not change while stored in a collection). This is the reason most of the times we prefer String objects as Key in many Map Collection objects. Immutable objects do not require an implementation of clone. Immutable objects allow hashCode to use lazy initialization, and to cache its return value. To crea...

package com.sbs.sort; /**  * @author Bhargava  *  * Time Complexity of Insertion Sort is O(n power 2) Worst Case  O(n) best case  * Recommended for Smallest array of elements.  * If you observe Array.sort() method in java.util api, if the array length is smaller than 7 our api is following     * insertion sort.  */ public class InsertionSort {     /**      * @param args      */     public static void main(String[] args) {         long intialTime = System.currentTimeMillis();         int[] array = { 24, 13, 9, 64, 7, 23, 34, 47 };                System.out.print(" Befor Sorting [ ");         for (int j = 0; j < array.length; j++) {       ...

Strings can be defined in Java in two ways. 1. String Literals 2  Traditional way(using 'new' operator) String Literals If a String is created by using String literal notation, memory will be allocated directly in string pool. String pool is subset of Heap memory (Where objects will be created). e.g. String companyName = "Surimenus";      String empName= "Bhargav";       Using 'New' Operator If a String is created using new operator, memory will be allocated in Heap Memory not in String pool. e.g. String companyName = new String("Surimenus"); String empName= new String("Bhargav"); String Pool vs Using 'new' Operator String which are created in String pool will re-reference by reference which contains the same content. For example consider the following. String cn1 = "Surimenu"; String cn2 = "Surimenu"; In the above scenario cn1 and cn2 references having the same content and these are created in Strin...

Certificates Certificates basically two categories. Self Signed Certificates  - will create by self CA Certificates  - will be  provided by Third party vendor with robust algorithms Depends on the location of installing the certificate these are two types 1. Public Key Certificates (Client Side) 2. Private Key Certificates (Server Side) Self Signed Certificates   If any one is using self signed certificates in their applications they have to make sure both server side and client side certificates are in sync. Other wise we should be ready to face SSLHandShake Exceptions. These will be preferable mostly for lower environments not for production. CA certificates  If you install CA certificates on server side, client side certificates are installed automatically whenever they access the server. So in production for CA certificates there is no need to install the client side certificates. We can generate a Self Signed Certificate using Java Key tool JAVA_HOME/bi...

Time out Any client(or source) which is unable to connect to the server (or Destination) in a specified time, then requests will automatically gets time outs. Port Port numbers allow different applications on the same computer to utilize network resources without interfering with each other. Port numbers most commonly appear in network programming, particularly socket programming. Sometimes, though, port numbers are made visible to the casual user. For example, some Web sites a person visits on the Internet use a URL like the following: http://www.appdomain.in:80/ In this example, the number 80 refers to the port number used by the Web browser to connect to the Web server. Normally, a Web site uses port number 80 and this number need not be included with the URL (although it can be). Port 80 is the default port for HTTP Socket Each and every communication from one application to another application should happen through sockets. Socket is gateway to send/receive information from one a...

/**  * Date Util might be useful in your daily activities.  */ package com.sbs.dateutil; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; /**  * @author bhargav  *  */ public class DateUtil {     /**      *      */     private DateUtil() {     }     /**      * @param args      */     public static void main(String[] args) {         //Date date = new Date();         //Another way to get the current date from Calender object is         Date utilDate = Calendar.getInstance().getTime();                 System.out.println("Default Util Curent Date and time :" + utilDate);      ...