Once again, BlueJ’s uncluttered presentation doesn’t stand between you and the task at hand.Īs mentioned above, BlueJ can create a test class from a class icon’s right-click menu. When, during execution, the breakpoint is triggered, BlueJ’s debugger pop-up opens, showing threads, call stack, lock static, and instance variables, as well as the familiar debugging controls (step, step into, continue, and stop). In the editor, just click in the column to the left of the targeted source code line.

You can set debugger breakpoints in BlueJ the same way you would in other IDEs. You can also execute individual object instance methods dialogs appear (as above) for entering input arguments and displaying return values.īlueJ wouldn’t be a complete IDE without a debugger. As with classes, you can right-click the object icon and examine the object’s contents. If you instantiate a class, an icon representing the new object appears in the object bench. Enter the inputs, click OK, and another dialog materializes, showing the return value and its data type. Choose to execute a class method and a dialog pops up, prompting you for the method inputs. In the foreground, an inspector window reveals the content of an instantiated CatView object.Ĭlasses can be individually compiled you don’t have to rebuild an entire project if you’ve modified a single class. The editor window in the background shows scope highlighting in action. Here, BlueJ’s interactivity takes center stage. Right-click on a class in the workbench, and a new menu appears that-depending on the nature and makeup of the class-lets you compile the class, inspect its contents, create a corresponding test class (more on this later), execute a class method, or instantiate an object of the class. Code structure is made instantly apparent. With scope highlighting, nested blocks of code are literally highlighted in different colored backgrounds, so you can quickly see the area covered by a method within a class, a for loop within a method, an if statement within that for loop, and so on. Project classes appear in the workbench as a kind of pared-down UML diagram, and while BlueJ is not a full-blown visual development environment, it’s enough of one so that you can see the relationships among entities in your program, but not lose sight of the code.ĭouble-click on a class icon in the workbench, and its source opens in the editor, where another visual assist is revealed: scope highlighting. Buttons on the toolbar let you create a class, define an inheritance relationship, or compile a class. Open a project in BlueJ and you’re presented with a refreshingly sparse window: menu bar across the top, toolbar to the left of a large workbench area, and a smaller object bench pane below. I later learned that BlueJ had been installed on the Raspberry Pi since 2015.

I first became aware of BlueJ (and Greenfoot) when I found them pre-installed on a Raspberry Pi 4 that I had gotten last year. Earlier, 32-bit versions exist, but they are no longer being developed. The current version of BlueJ (4.2.2 at the time of this writing) requires JDK 11 or later, and as such must be run on a 64-bit operating system. BlueJ also comes in a generic form: packaged as a JAR file so that BlueJ can be installed on any system that supports Java. When Java appeared, the tool was rebuilt using Java as the language and the name was changed to BlueJ.Įditions of BlueJ exist for Linux, MacOS, and Windows. At that time, it was both a development environment and a language. Learn Java with BlueJīlueJ first appeared in 1999, named simply Blue.

Consequently, both provide an easy introduction not only to the Java language, but to the tools and techniques needed to build applications in that language. In fact, as Neil Brown, the lead developer explains, BlueJ’s and Greenfoot’s features are “.revealed as users come to them.” You are not thrown into the deep end of the pool. The creators of BlueJ and Greenfoot selected the feature set and interface design to not overwhelm beginners. They are the product of a team based at King’s College in London (though team members have, at times, been affiliated with universities in Australia and Denmark). Your chosen development tool is as impenetrable as the language it’s supposed to help you with.Įnter BlueJ and Greenfoot, two IDEs very specifically designed for beginners. You choose one, download and install it, and in a very short time you realize that you now have two things to learn: Java and the IDE. Several popular, free Java IDEs are available: Eclipse, NetBeans, and the community edition of IntelliJ, for example. A single application in which you can edit, build, run, debug, and deploy your soon-to-be-written Java application. Ok, first things first: You need one of those integrated development environments (IDEs) you’ve read about. But, you take a deep breath and resolve to give it a go. It might even seem impenetrable if you’re a new programmer.

Greenfoot sound