How to take a screenshot of your desktop

This tutorial shows you how to capture a screenshot of your desktop.

import java.io.File;
import javax.imageio.ImageIO;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.image.BufferedImage;

try {
  Robot robot = new Robot();
  //I assume that the size of the image you want is 300 x 200
  BufferedImage img = robot.createScreenCapture(new                                                Rectangle(300,200));
  //I am saving the image as a png image
  //But you can use any other image formats like bmp, jpg etc.
  ImageIO.write(img, "png", new File("D:/screen.png"));
} catch (Exception ex) {
  ex.printStackTrace();
}

Ok. But sometimes you may want to capture the whole screen.
So you have to import Toolkit first.

import java.awt.Toolkit;

Your new code will look like this.

try {
  Robot robot = new Robot();
  Rectangle rect = new Rectangle( Toolkit.getDefaultToolkit().getScreenSize());
  BufferedImage img = robot.createScreenCapture(rect);
  ImageIO.write(img, "png", new File("D:/screen.png"));
} catch (Exception ex) {
  ex.printStackTrace();
}

How to execute a DOS command using Java.

As you know "mkdir" is the DOS command which lets you create a new folder at a given location.
In order to create a folder named as "MyFolder" in your "C:" drive you can use the following command.
>>mkdir c:\MyFolder

But in java you need to do an additional work to execute this command.
So you have to add "cmd /c" to your command.
Following code creates a new folder named as "MyFolder" in drive "C:".

String cmd = "cmd /c";
String command = "mkdir";
String folderName = "C:\\MyFolder";
Runtime.getRuntime().exec(cmd + " " + command + " " + folderName);

But what will happen if your folder name contains space characters.
For an example if the name of your folder was "My Folder" instead of "MyFolder".
Then you should add extra double quotes and escape them as below.

String folderName = "C:\\\"MyFolder\"";

How to replace a character or a word at a given position in Java.

Lets assume that you want to replace the 7th character ("-") in following string with "*" character.
Then you can do it as below.

String s = "I*LIKE-JAVA BUT MY FRIEND LIKE .NET.";
System.out.println(s.substring(0,6) + "*" + s.substring(6 + 1));

Note that in above string there are two occurances of the word "LIKE".
If you want to replace the first occurances of the word "LIKE" with the word "LOVE" then you can do it as below.

String s = "I*LIKE-JAVA BUT MY FRIEND LIKE .NET.";
System.out.println(s.substring(0,2) + "LOVE" + s.substring(2 + 4));

Below example shows you how to remove a character at a certain position.
In this example we remove the "*" characterfrom the text.

String s = "WE*LIKE";
System.out.println(s.substring(0,2) + s.substring(3));

If you want to remove all the "*" from the string "I*LOVE*JAVA" then you can use below method.

String initialString = "I*LOVE*JAVA";
String result = "";
for (int i = 0; i < initialString.length(); i ++) {
 if (initialString.charAt(i) != '*') {
  result += initialString.charAt(i);
 }
}
System.out.println(result);

Read a file line by line

 In this example I explain how to read a file line by line and add the lines to a List.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JOptionPane;

public static void main(String[] args) throws IOException {
  String fileName = "c:\\camera.log"; \\Path to your file
  FileReader reader = new FileReader(fileName);
  BufferedReader buffReader = new BufferedReader(reader);
  List linesList = new ArrayList();
  String line;
  while((line = buffReader.readLine()) != null){
    linesList.add(line);
  }
  //For this example I just show a message box to display the content of the file.
  JOptionPane.showMessageDialog(null, linesList.toArray());
}

Increase the size of an array

In Java there is no direct way to increase the size of an array after is is defined.
In this post I will show you how to do this easily.
Think you have following array. The size of this array is 1.

String[] arr = new String[1];

Now you can increase the size of your array like this.(replace the word "NEW_SIZE" with your new size)

arr=(String[]) Arrays.asList(arr).toArray(new String[NEW_SIZE]);