How to Get Class Path in a Java Application

Class Path is the Path used to find directories and JAR archives containing class files. Elements of the class path are separated by platform-specific characters. To get class path from a running java application, you may use the getProperty() method in System class. The following java code will show you how to get class path in java.

String classpath=System.getProperty("java.class.path");
System.out.println("Class path="+ classpath);

Why FileOutputStream or BufferedWriter Does Not Write New Line to File

The new-line character is system dependent. It depends on operating system. It can be \n, \r, \r\n or something else depending on the operating system. So, when we are writing a cross platform java program, it is important to take care when we use a line separator or new line character. It is always safe to use system specific line separator provided by JVM. You can get the system specific newline character in different ways.

Method 1:

System.lineSeparator() instead of new line character. The java method Sytem.lineSeparator() returns the newline character (line separator) as a strong. If you are appending a string on another with a line separator in between, it can be done as follows.

line1+System.lineSeparator()+line2

Method 2:

You can also get the line separator using the getProperty() method with property key line.separator.

System.getProperty("line.separator");

Method 3:

If your are using a BufferedReader object to write text into a file, you can use the newLine() method to write a newline into the file. If br is a BufferedReader object, br.newLine() will write a newline (line separator) into the file.

Method 4:

If you want to get the line separator as a character, you may use the static member Character.LINE_SEPARATOR. It returns the Unicode newline character.

How to Make a Timer Controlled Progress Bar in Java

timer controlled progress bar in java

For some applications we require to use timer and progress-bars. Java has a swing class called
JProgressBar to create progress bars. It can have horizontal or vertical orientation. We can set the maximum and minimum values for JProgressBar. It can also have an indeterminate state in which the progressbar does not show a definite value and plays an animation to show that the process is in progress. JProgressBar can be used in indeterminate mode when neither can you determine how long a process would take to complete nor can you track its progress. In some other cases, you may have to use timers. Java provides a Timer class (Java.util.Timer). But you can create a very simple and flexible timer if you want. If the timer does not have crucial importance, you can use a thread that sleeps for every one second as a timer. I have been using such threads as timers for a long time and never failed. Such timers may fail (although very rarely) when the processor has very heavy workload.

Whatever, in a simple example, we will see how to create a timer using thread and how to use JProgressBar. In this example we control the JProgressBar using the timer. The progress in JProgressBar is set calling the method setValue(). In this example we are using a 1 minute timer. The progress bar should show the progress of timer. The java code for timer controlled JProgressBar is as follows:

Problem With JProgressBar setValue Method? JProgressBar Value Not Updating - Solution

I had a problem with a JProgressBar. I called setValue() method of the java swing class JProgressBar for an object but the JProgressBar is still sowing zero progress.This problem may occur for many people. People use the words:

Jprogressbar setvalue not upadting

jprogressbar.setvalue not working

jprogressbar setvalue problem

for googling this problem. All these keyword combinations have a presumption that the problem is with java not on our part, Actually, the problem is on our part but it is a silly mistake. I know two reasons for such problem.

Java Program to Send Image between Computers using UDP and Display it

Java program to send image file over network using UDP

This was one of my experiments in Networking Lab. The aim was to write a java program to send a
picture (image) from a computer to another via network using UDP protocol and to display it at the receiving end. Simply, this is the java code to make a java application which can send images from one computer to another over a network. The program uses UDP (User Datagram Protocol). For both the computers (on either ends) the same code is enough. This app can act as a image sender or a receiver. The program uses a Progress bar (JProgressBar) to show the progress of the data transfer. Remember, transferring files over UDP is not easy because UDP does not guarantee ordered delivery, and not even successful delivery. So, here in this program, to ensure ordered delivery, the sender sends next chunk of data (DatagramPacket) only after receiving an acknowledgement for last sent packet. For acknowledgement, i used a string "ACK".

Chat Room Application using UDP in Java

Java Chat room application using UDP

The following is a Java program for chatting. This chatting application uses UDP (User Datagram
Protocol) for chatting. The application gives you to options. One is to create a new chat room and the other is to join a chat room. The one who creates the chat room acts as a server for the chatroom. Others can join this chatroom id they know his IP address. This simple java chat room application is enough for server and clients. The GUI is basic one and not too attractive. Also i have used JOptionPane to reduce code. You may make improvements to the code. The chat rooms are not password protected. Anyone who know the server's IP address are granted access to the chat room. If you wish, you may improve the program. This Group chat application using java can be used in Local area networks. This code for java group chat program can be modified to enable chatting in multiple chat rooms. Try it.

How to download a file from internet Using java if URL is Given

Let us see how to download a file from internet in java. It is so simple. The following java program is a program which will download any file if the URL to the file to be downloaded is given. It also asks the user for destination to save the file. It displays the file size also. It also prints (displays) the progress of download. It uses the classes HttpURLConnection, URL, FileOutputStream, JFileChooser etc. The following java code is a simple java program to download a file from internet using URL. Here in this case, user has to give the file name and extension.

How to Easily Copy a File to Another File or Location in Java

The Files class in java has many useful static methods to copy and move files, create temporary files or folders etc. To copy a file from one location to another in Java, there is a static method copy in Files class. The Files class is in java.nio.file package. The method Files.copy() takes three arguments (parameters) : Path of source file (as object of Path class), Path of destination file ( as object of Path class ) and an option parameter. The option parameter can be one of the following:

StandardCopyOption.REPLACE_EXISTING
If the target file exists, then the target file is replaced.

StandardCopyOption.COPY_ATTRIBUTES
Attempts to copy the file attributes associated with this file to the target file. The exact file attributes
that are copied is platform and file system dependent and therefore unspecified.

StandardCopyOption.NOFOLLOW_LINKS
Symbolic links are not followed. If the file is a symbolic link, then the symbolic link itself, not the target of the link, is copied.

You have to import java.nio.file.StandardCopyOption to use option parameters.

try{
File sourcefile=new File("audio.mp3");
File destination=new File(System.getProperty("java.io.tmpdir")+"\\temp.mp3");
Files.copy(sourcefile.toPath(),destination.toPath(),StandardCopyOption.COPY_ATTRIBUTES);
} catch (IOException ex) {
ex.printStackTrace();
}

For the copy method, there are two other overloaded method definitions. In one, instead of source file's path, inputstream is the first parameter and the rest are same. For the other overloaded definition, an outputstream object is the second parameter instead of destination path object and the rest are same.

Similarly, to move a file from one location to another, there is a method move() in Files class. The parameters of this method is also same as those of copy method.

How to Get Path to Temp Directory for Current User in Java

In some cases, you may need to create temporary files. It is preferred to create temporary files and folders in the current user's temporary folder (temp directory) because, the user will be able to clean unwanted files. To get the path to the temp folder of current user, java provides a property key to be used with

System.getProperty()

. it is

"java.io.tmpdir"

.

The following code displays the path to the temporary folder for the current user.

System.out.println("temp directory ="+System.getProperty("java.io.tmpdir"));

How to Get Center Point of Screen in Java

If you want position your JFrame in center of screen, there is method for that. Read this post:

How to Set JFrame in Center of Screen

The LocalGraphicsEnvironment in Java will give you the center point of the display or screen. There is a static method getLocalGraphicsEnvironment() in GraphicsEnvironment class. To get the center point of the screen, you may use the following java code:

Point centre=GraphicsEnvironment.getLocalGraphicsEnvironment().getCenterPoint();

You should include these import statements in the file.

import java.awt.Point; import java.awt.GraphicsEnvironment;