Compile the Source File into a .class File

To compile your source file, choose Build Build Main Project from the IDE's main menu.
The Output window opens and displays output similar to what you see in the following figure:
Output window showing results of building the HelloWorld project.
If the build output concludes with the statement BUILD SUCCESSFUL, congratulations! You have successfully compiled your program!
If the build output concludes with the statement BUILD FAILED, you probably have a syntax error in your code. Errors are reported in the Output window as hyper-linked text. You double-click such a hyper-link to navigate to the source of an error. You can then fix the error and once again choose Build Build Main Project.
When you build the project, the bytecode file HelloWorldApp.class is generated. You can see where the new file is generated by opening the Files window and expanding the Hello World App/build/classes/helloworldapp node as shown in the following figure.
Files window, showing the generated .class file.
Now that you have built the project, you can run your program