Problem Solving with Algorithms and Data Structures using Kotlin The Interactive Edition

Here’s the minimal prototypical Kotlin program:

Let’s go through this line by line.

Line 1: Every program that you want to run must have a function named main; the operating system will start running your program by calling this method.

Line 2: The function body, which, in this case, consists of a single statement that prints the words Kotlin works!. This function prints its argument followed by a newline—ln stands for line.

When you save this program, you can use any filename you wish, though it must end with the extension .kt. For example, we can save this as ExampleProgram.kt.

Most Integrated Development Environments are set up so that you can compile and run your Java programs with the click of a button or a menu choice. It is also possible to run a Kotlin program from the command line. Here is an example of running the preceding program from a Linux shell where the $ is the command line input prompt:

$ kotlinc ExampleProgram.kt
$ ls
ExampleProgramKt.class ExampleProgram.kt
$ kotlin ExampleProgramKt
Java works!

The kotlinc command invokes the Kotlin compiler. It translates the source code into bytecode, a form which the runtime system can execute. This bytecode file is given almost the same name as the original file, but it adds Kt to the main part of the filename, and the extension is .class. So in this case, after compiling, we have a new file named ExampleProgramKt.class. Since there are no errors in the program, there is no output shown on the screen after running kotlinc (“no news is good news”).

The ls command lists the files in the current directory; you don’t need to do this command, but it’s here to show you that, after compiling, you have two files: ExampleProgramKt.class (the bytecode) and ExampleProgram.kt (the source code).

The kotlin command runs the program. You give it the main part of the name of the compiled bytecode file (in this case, ExampleProgramKt).