Java

Javac/Java searching algorithm for other classes

Mallik4 Comments

With this post, I would like to explain how exactly the Java/Java will search for its dependencies in the project or application level. Java Applications can be run using the command line or in the Web/Application servers. For both the scenarios will be covered as below:

When you are accessing standalone application using command prompt, below will be the search criteria steps:

Step 1: The first place that look in the directories that contains the classes that come with Java SE.

Step 2: The classpath that declared as command line options for either Java/Javac. Since the classpath declared in command line options override the classpath declared in command line options persists only for the length of the invocation.

Step 3: Looks for the the default classpath that declared as System Environment Variables.

When you are accessing the application from Web or application servers, below will be the search criteria steps:

Step 1: The first place that look in the directories that contains the classes that come with Java SE.

Step 2: If the dependencies not able to identify in the JRE lib folder, then it will be looked into the Application lib folder.

Step 3: If the dependencies not able to fine in above two steps, then it will be looked into Web/App server lib folder.

 

Other Useful Links:

Differences between Object and Instance
Difference between Abstract Class and Interface:
Threads Interview questions in Java
Access Specifiers in Java
Avoid nested loops using Collection Framework in Java

Example Program – Armstrong Number

MallikLeave a comment

Below sample programs finds whether the given number is an Armstrong Number or not.

An Armstrong number of three digits is an integer such that the sum of the cubes of its digits is equal to the number itself. For example, 371 is an Armstrong number since 3**3 + 7**3 + 1**3 = 371. Few more Examples for the Armstrong numbers are : 153, 371, 9474, 54748.

 

package in.javatutorials;

/**
* @author malliktalksjava.in
*
*/
public class ArmstrongNumber {

/**
* @param inputNumber
* @return boolean true/false will be return
*/
public static boolean isArmstrong(int inputNumber) {
String inputAsString = inputNumber + “”;
int numberOfDigits = inputAsString.length();
int copyOfInput = inputNumber;
int sum = 0;
while (copyOfInput != 0) {
int lastDigit = copyOfInput % 10;
sum = sum + (int) Math.pow(lastDigit, numberOfDigits);
copyOfInput = copyOfInput / 10;
}
if (sum == inputNumber) {
return true;
} else {
return false;
}
}

/**
* @param args
*/
public static void main(String[] args) {
int inputNumber = 153;
System.out.print(“Enter a number: “);
boolean result = isArmstrong(inputNumber);
if (result) {
System.out.println(inputNumber + ” is an armstrong number”);
} else {
System.out.println(inputNumber + ” is not an armstrong number”);
}
}
}

 

Example program to reverse a Number in Java

Mallik2 Comments

 

package in.javatutorials;

public class ReverseNumber {

public static void main(String[] args) {
System.out.println(“The reversed number is ” + reverse(1234));
}

public static int reverse(int input) {
int result = 0;
int rem;
while (input > 0) {
rem = input % 10;
input = input / 10;
result = result * 10 + rem;
}
return result;
}
}

 

How to find count of duplicates in a List

Mallik7 Comments

There are many different ways to find out the duplicates in a List or count of duplicates in a List object. Three best ways have been implemented in the below sample class. I suggest to go with 2nd sample, when there is a requirement in your project.

package in.javatutorials;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class CountOfDuplicatesInList {

public static void main(String[] args) {

List<String> list = new ArrayList<String>();
list.add(“a”);
list.add(“b”);
list.add(“c”);
list.add(“d”);
list.add(“b”);
list.add(“c”);
list.add(“a”);
list.add(“a”);
list.add(“a”);

// Find out the count of duplicates by passing a String – static way
System.out.println(“\n Output 1 – Count ‘a’ with frequency”);
System.out.println(“a : ” + Collections.frequency(list, “a”));

// Find out the count of duplicates using Unique values – dynamic way
System.out.println(“\n Output 2 – Count all with frequency”);
Set<String> uniqueSet = new HashSet<String>(list);
for (String temp : uniqueSet) {
System.out.println(temp + “: ” + Collections.frequency(list, temp));
}

// Find out the count of duplicates using Map – Lengthy process
System.out.println(“\n Output 3 – Count all with Map”);
Map<String, Integer> map = new HashMap<String, Integer>();

for (String temp : list) {
Integer count = map.get(temp);
map.put(temp, (count == null) ? 1 : count + 1);
}
for (Map.Entry<String, Integer> entry : map.entrySet()) {
System.out.println(“Key : ” + entry.getKey() + ” Value : ”
+ entry.getValue());
}
}
}

 

Other Useful Links:

Avoid nested loops using Collection Framework in Java

Replace special characters in a String using java

Singleton Design pattern in JAVA

Convert Array to Vector in Java

How to Copy an Array into Another Array in Java

Tips to follow while doing java code

How to Create a Thread Using Runnable Interface

Mallik1 Comment

In Java, a Thread can be created by extending to a Thread class or by implementing the Runnable Interface. In below example, I have tried to create the thread by implementing Runnable interface.

package in.javatutorials;

public class CreateThredByRunnable {

public static void main(String[] args) {
Thread myThreadA = new Thread(new MyThread(), “threadA”);
Thread myThreadB = new Thread(new MyThread(), “threadB”);
// run the two threads
myThreadA.start();
myThreadB.start();

try {
Thread.currentThread().sleep(1000);
} catch (InterruptedException e) {
}
// Display info about the main thread
System.out.println(Thread.currentThread());
}

}

class MyThread implements Runnable {
public void run() {
for (int i = 0; i < 5; i++) {
System.out.println(Thread.currentThread());
}
}
}

 

Other Useful Links

Threads Interview questions in Java

Multi-Threading Interview questions

Mallik3 Comments

Thread concept is the most important topic for all the interviews. This post contains most important interview questions on Thread concepts. The answers for these questions will be covered in further posts.

  1. What is a thread ? What are the ways we have in Java to create a thread ?
  2. Write a program to create a thread using Thread class or Runnable interface.
  3. Which is the default thread that runs in every java program internally ?
  4. What is the difference between extends Thread or implements Runnable ? Which one is more useful.
  5. What is thread deadlock? Describe it.
  6. Which methods are used in thread communication.
  7. How can you set priorities to a thread ? And, what is the default priority number of a thread ?
  8. What is a Thread Scheduler ?
  9. What is a Daemon Thread ?
  10. What id thread life cycle ? Explain.
  11. How can you improve communication between two threads?
  12. What is ThreadGroup ? What are the benefits of ThreadGroup ?
  13. What is the difference between Process and Thread ?
  14. What is the difference between notify() and notifyAll() methods ?
  15. Explain some of the methods in Thread class.

JDBC Type Driver connection for MS SQL Server

MallikLeave a comment

Below is the sample program to connect to MS SQL Sever using JDBC type 4 driver:

package in.javatutorials;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

/**
* @author JavaTutorials.in
*
*/
public class MSSqlDBConnection {

/**
* initialize the connection object
*/
private static Connection connection = null;

/**
* Create the database connection and return the same
*
* @return connection Connection
*/
public static Connection getDbConnection() {

// if required, below variables can be read from properties file
String username = "sqlusr";
String password = "sqlpasswrd";
String connStr = "jdbc:sqlserver://:1433;instanceName=SQLEXPRESS;databaseName=test";
try {
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");

connection = DriverManager.getConnection(connStr, username,
password);
} catch (ClassNotFoundException classNotFoundExcep) {
classNotFoundExcep.printStackTrace();
} catch (SQLException sqlExcep) {
sqlExcep.printStackTrace();
}
return connection;
}

/**
* Close the connection if exists, this method can be called once
* transaction is completed, so that it will close the connection
*/
public static void closeConnection() {
if (connection != null) {
try {
connection.close();
} catch (SQLException sqlExcep) {
sqlExcep.printStackTrace();
}
}
}

public static void main(String[] args) {
System.out.println("Print the Database conn object : "
+ getDbConnection());
}
}

Avoid nested loops using Collection Framework in Java

Mallik2 Comments

High performance is essential for any software implemented in any programming language. And, loops plays major role in this regard. This post explains how to avoid the loops using Java’s Collection framework.

Below are the two Java programs to understand how the performance could be increased using the Collection framework.

Using nested loops

package in.javatutorials;

/**
* Finds out the Duplicates is String Array using Nested Loops.
*/
public class UsingNesteadLoops {
  private static String[] strArray = { "Cat", "Dog", "Tiger",     "Lion", "Lion" };

  public static void main(String[] args) {
   isThereDuplicateUsingLoops(strArray);
  }

  /**
   * Iterates the String array and finds out the duplicates 
   */
   public static void isThereDuplicateUsingLoops(String[]     strArray) {

   boolean duplicateFound = false;
   int loopCounter = 0;

   for (int i = 0; i < strArray.length; i++) {
   String str = strArray[i];
   int countDuplicate = 0;

   for (int j = 0; j < strArray.length; j++) {
      String str2 = strArray[j];
      if (str.equalsIgnoreCase(str2)) {
         countDuplicate++;
      }
      if (countDuplicate > 1) {
         duplicateFound = true;
         System.out.println("Duplicates Found for " + str);
      }
      loopCounter++;
   }// end of inner nested for loop

   if (duplicateFound) {
    break;
   }
}// end of outer for loop

System.out.println("Looped " + loopCounter + " times to find the result");
}

}

If we run the above program, it will be looped 20 times to find out the duplicates in the string array which has the length of 5. Number of loops increases exponentially depending on size of array, hence the performance takes a hit. These are not acceptable to use in applications which require high performance.

Without using nested loops

package in.javatutorials;

import java.util.HashSet;
import java.util.Set;

/**
* Finds out the Duplicates is String Array using Collection.
*/
public class AvoidNesteadLoopsUsingCollections {

private static String[] strArray = { "Cat", "Dog", "Tiger", "Lion", "Lion" };

public static void main(String[] args) {
 isThereDuplicateUsingSet(strArray);
}

/**
* Iterates the String array and finds out the duplicates
*/
public static void isThereDuplicateUsingSet(String[] strArray) {
  boolean duplicateFound = false;
  int loopCounter = 0;
  Set setValues = new HashSet();

  for (int i = 0; i < strArray.length; i++) {
    String str = strArray[i];

    if(setValues.contains(str)){
        duplicateFound = true;
        System.out.println("Duplicates Found for " + str);
    }
    setValues.add(str);
    loopCounter++;

    if (duplicateFound) {
       break;
    }
   }// end of for loop

   System.out.println("Looped " + loopCounter + " times to find the result");
 }

}
  • Above approach takes only 5 loops to identify the duplicates in the same array.
  • It is more readable , easier to maintain and performs better.
  • If you have an array with 1000 items, then nested loops will loop through 999000 times and utilizing a collection will loop through only 1000 times.

Other Useful links:

Create a Dynamic web project using STS

Mallik4 Comments

Below steps explain the creating a dynamic web project using STS.

Step 1 : Select File -> New -> Other.

CreateWebproject

Step 2:  Select the Dynamic web project from the menu and click on Next button.

dynamixwebproject

 

Step 3: Give a name to Dynamic web project and click on Finish button.

namewbproject

 

Step 4: A new project will be created as below with web project structure

webprojectstructure

Java Source files can be kept into src folder other files can will be kept into the sub folders of the WebContent folder.

 

Replace special characters in a String using java

Mallik4 Comments

package in.javatutorials;

/**
* @author javatutorials
* @since version 1.0
*
* Below class replaces the special characters in a string with empty value
*
*/
public class ReplaceSpecialCharacters {

public static final String REG_EXPR = “[!\”#$%&'()*+-./:;<=>?@\\^_{|}~`,.\\[\\]]*”;

/**
* @param args
*/
public static void main(String[] args){
String str = “a – b +c^d!e+f g . h (Pvt) Ltd.”;
//Create class object and call replace special characters method
ReplaceSpecialCharacters rsc = new ReplaceSpecialCharacters();
String afterReplacing = rsc.replaceSpecialChars(str);
System.out.println(“After replacing special characters : “+afterReplacing);
}

/**
* @param string String
* @return string String
*/
public String replaceSpecialChars(String string){
string = string.replaceAll(REG_EXPR, “”);
while(string.indexOf(” “) != -1){
string = string.replaceAll(” “, ” “);
}

return string;
}

}