One of the most useful features of DrJava is the “Interactions Pane” at the bottom of the window. It provides the ability to try out code quickly, without having to write a class definition and save/compile/run the program. Figure 15.2.1 shows an example.
There is one subtle detail to note when using the Interactions feature. If you don’t end an expression (or statement) with a semicolon, DrJava automatically displays its value. Notice in Figure 15.2.1 how the variable declarations end with semicolons, but the logic expressions in the following lines do not. This feature saves you from having to type
System.out.println every time.
What’s nice about this feature is that you don’t have to create a new class, declare a
main method, write arbitrary expressions inside
System.out.println statements, save the source file, and get all of your code to compile in advance. Also, you can press the up/down arrows on the keyboard to repeat previous commands and experiment with incremental differences.