BLUEJ File

What are BLUEJ files and how to open them

Are you having problems opening a BLUEJ file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BLUEJ files.

What is a BLUEJ file?

A .BLUEJ file is a BlueJ Package file.

BlueJ package files record metadata about how a BlueJ project is laid out, how the package diagram in the BlueJ IDE is displayed, and the layout settings for targets (classes, interfaces, packages etc.) in the GUI. These files are used internally by the BlueJ environment when a project is opened, so BlueJ can restore package layout (positions, sizes) and editor‐window settings.

They are created by the BlueJ Java development environment when a project is saved. BlueJ reads them when opening the project to present the user's last arrangement of the package diagram and target icons as they were when the project was last closed or saved.

These files are plain-text formatted and begin with the ASCII signature "#BlueJpackagefile". They contain field names like PACKAGE.NUMDEPENDENCIES, PACKAGE.EDITOR.WIDTH and .HEIGHT, PACKAGE.EDITOR.X and .Y, TARGET1.NAME, TARGET1.TYPE, TARGET1.WIDTH, TARGET1.HEIGHT, TARGET1.X, TARGET1.Y, and also fields such as CLASSTARGET and PACKAGE.NUMTARGETS.

How to open BLUEJ files

Important: Different programs may use files with the BLUEJ file extension for different purposes, so unless you are sure which format your BLUEJ file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested six different BLUEJ openers which you will find listed below.

Last updated: August 24, 2026

Various apps that use files with this extension

These apps are known to open certain types of BLUEJ files. Remember, different programs may use BLUEJ files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about BLUEJ file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.