Importing Java libraries and exporting code in projects as a JAR file

We will now download a JAR file from the internet and use it in our project to create a JAR file for our project.

Open a web browser and search for download a junit.jar. This will take you to a link where you can download a JAR file. There are online repositories available where JAR files exist. One of the most reliable repositories can be found at http://www.java2s.com/Code/Jar/j/Downloadjunitjar.htm, where you can download any available JAR file. If you click on it, it should take you to the following page:

As seen in the preceding screenshot, you will find the junit.jar file and the different classes that are available in the JAR file also listed. You can right-click on the save (floppy disc) symbol to save the file on your system.

Once the file is downloaded, extract it into a junit.jar file. You can then add it to your project with the following steps:

1. Create a new project on NetBeans, for example, HelloWorld.
2. Since the new project will not have the junit.jar file, go to Properties by right-clicking on the project, as shown in the following screenshot:

 

3. Go to the Libraries | Add JAR/Folder option and provide the location of where this junit.jar file is, as follows:

4. Once done, click on Open and it will be added to your project:

5. Now the JAR file has been added to the project, we can use the junit.jarfile in animportstatement.We can alsoimportindividual packages, as shown in the following screenshot:

6. If you want to use all of the classes in framework, you just have to write the following code:

import junit.framework.*;

7. Now, let's use the following code to print the output Hello World:

package helloworld;

/**
 *
 * @author admin
 */
import junit.framework.*;
public class HelloWorld {

 /**
 * @param args the command line arguments
 */
 public static void main(String[] args) {
 // TODO code application logic here
 System.out.println("Hello World"); 
 } 
}

8. After running the preceding code, you should get an output similar to the following:

If you want to create a JAR file for this project, please perform the following steps:

1. Go to Run and select Clean and Build Project (HelloWorld) to build your project:

2. Once building the HelloWorld project is complete, the Output window will say BUILD SUCCESSFUL, as shown in the following screenshot:

3. To check if the JAR file been created or not, go to Windows Explorer and navigate to your project's location, which you received from the previous output:

4. Open the project folder, in our case HelloWorld, and go into the dist folder, as follows:

5. In the dist folder, you will find the JAR file (HelloWorld.jar), which you can use and where there will be a lib folder. This will contain the junit.jar file that is being used by the HelloWorld.jar file:

This means that whenever you use any JAR files in your project, they will be stored in the lib folder of your JAR file.