BlueJ is a free Java IDE built for teaching, with visual class diagrams and interactive objects, from the University of Kent and Monash University.
BlueJ is a free, education-focused integrated development environment for Java, built around visualizing class structure and letting students interact directly with objects while they learn to program. Development began in 1999 at Monash University by Michael Kolling and John Rosenberg, as a successor to an earlier teaching tool called Blue, with the first release on August 23, 1999.
BlueJ became closely tied to the University of Kent in the United Kingdom, where it supported introductory object-oriented programming courses, and is now maintained by King's College London with support from Oracle. James Gosling, the creator of the Java language, has publicly named BlueJ as one of his favorite IDEs.
Because BlueJ is aimed squarely at teaching, it deliberately simplifies parts of the software development workflow that full-scale professional IDEs make complex, prioritizing visual clarity and direct interaction with objects over the breadth of features found in tools like IntelliJ IDEA or Eclipse.
BlueJ's main window displays an application's classes as a UML-like diagram, and students can create objects directly from that diagram, inspect their internal state, call methods on them interactively, and pass objects as parameters, all without first writing a main method or test harness.
The Code Pad lets users evaluate Java expressions immediately without compiling a full program, functioning as a graphical shell or REPL for Java that is specifically suited to experimentation and learning. The source code editor includes scope coloring, which visually highlights nested code blocks to help beginners follow program structure.
As of version 6.0.0, released July 1, 2026, BlueJ added support for the Kotlin programming language alongside its original Java focus, broadening the languages instructors can teach with the same visual, object-interactive workflow.
BlueJ is completely free to download and use, with no purchase price, subscription, or commercial licensing tier. It is distributed under the GNU General Public License version 2 with the Classpath Exception, with copyright held by Michael Kolling and John Rosenberg.
Because it is free and open source, schools, universities, and individual learners can install BlueJ on an unlimited number of machines without licensing costs, which has been a significant factor in its widespread adoption in introductory programming courses.
BlueJ requires a 64-bit operating system, supporting Windows 8 or later, macOS 11 or later, and Ubuntu or Debian 20.04 or later; users on older 32-bit hardware can still run the free legacy 4.1.4 release.
Yes, BlueJ is completely free to download and use, distributed under the GNU General Public License version 2 with the Classpath Exception.
BlueJ is used primarily for teaching object-oriented programming, especially Java, by visualizing class structure and letting students interact directly with objects.
BlueJ was created by Michael Kolling and John Rosenberg, with development starting in 1999 at Monash University, and later strong ties to the University of Kent; it is now maintained by King's College London.
Yes, as of version 6.0.0, released July 1, 2026, BlueJ added support for the Kotlin programming language alongside Java.
BlueJ supports 64-bit Windows 8 or later, macOS 11 or later, and Ubuntu or Debian 20.04 or later; older 32-bit systems can use the legacy 4.1.4 release.
Yes, BlueJ was specifically designed for programming beginners, with features like an interactive object bench and scope-colored editor to simplify learning object-oriented concepts.
Yes, BlueJ continues to be actively maintained, with version 6.0.0 released July 1, 2026.
No, BlueJ is designed for teaching and learning rather than large-scale production development, so most learners move to a professional IDE like IntelliJ IDEA or Eclipse as their projects grow.