2.17 Printing the indexes array

Juppies 2 by Dr Heinz M. Kabutz

We want to show the indexes before and after shuffling. The easiest way is to print this to the console. What on earth is a console? Well, a very long time ago, computer systems were just letters and numbers on a screen. We had no beautiful graphical user interfaces with millions of colours and 10 million pixels. When I was in my 2nd year of university, that's what we had. 10 students at a time would connect via text terminals to a single 80386 machine running IBM's AIX. Single CPU of course. We had a graphics course. Go figure. Since our screens could only show text, we had to print our graphics assignments to the shared dot-matrix printer. When we say that we want to print some output, that would mean sending it to our Command Prompt on Windows, or our Terminal if we are using Mac OS X. In NetBeans we will see the output at the bottom of the IDE in the "Output" tab.

To print information to the standard output, we use the shortcut "soutv" followed by the tab button. This then picks the closest variable (either local variable, parameter or field) and generates the following code for us:

  System.out.println("variable = " + variable);

Very nice!

(The soutv shortcut is precisely the same as IntelliJ's which makes it easy swapping between NetBeans and IntelliJ)

Note: NetBeans is a platform and a framework that we can use to create rich client applications. For example, JVisualVM is a free performance profiler that is built on top of NetBeans platform. NetBeans is not only an IDE for writing code. Because it is open source, we can use it for our rich GUI applications. IntelliJ is only an IDE - which it does remarkably well.

We now run the code and see strange output like indexes - [I@5d624da6. What is that all about? This is the default behavior if we print an array to the console. The [I means it is an int array, and the funny hexadecimal number after the "@" looks like a memory location, but it is not. This is the hash code of the object. We will learn about this in a later lesson. Obviously this did not give us the output that we were hoping for. We thought it would print [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].

When we run the test, we notice that the output is always the same shuffled order of [4, 8, 9, 6, 3, 5, 2, 1, 7, 0]. What's with that? Turns out we must have some mistake in our shuffle() method that causes it to not be very "random".

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Table of Contents

• 0.1: Programming is a team sport - source control
• 0.2: Creating an account on GitHub
• 0.3: Forking the Juppies2 repository from kabutz
• 0.4: Oracle JDK
• 0.5: Oracle OpenJDK
• 0.6: Azul's Zulu OpenJDK
• 0.7: Installing the Oracle OpenJDK
• 0.8: Integrated Development Environments (IDEs)
• 0.9: Downloading Apache NetBeans
• 0.10: Loading our Juppies2 Project in Apache NetBeans
• 0.11: Running the AnagramGame with Apache NetBeans
• 0.12: Downloading IntelliJ IDEA Community Edition
• 0.13: Installing IntelliJ IDEA Community Edition
• 0.14: Running the AnagramGame with IntelliJ IDEA Community Edition
• 0.15: Downloading and Installing Eclipse
• 0.16: Running the AnagramGame with Eclipse
• 1.1: AnagramGame Project Structure
• 1.2: WordLibrary
• 1.3: Swing User Interface (UI)
• 1.4: Buffer Overflows
• 1.5: Demo of New Word Button
• 1.6: Demo of Guess Button
• 1.7: StaticWordLibrary Structure
• 1.8: StaticWordLibrary Details
• 1.9: Changing the Size of Our StaticWordLibrary
• 1.10: How my Buffer Overflow Wiped my Colleague's Hard Disk
• 1.11: Adding Our Own Words to the StaticWordLibrary
• 1.12: WordLibraryTest With JUnit
• 1.13: Java's For Loop
• 1.14: Testing That Words Are Anagrams
• 1.15: Running JUnit
• 1.16: isAnagram() Method
• 1.17: Fixing StaticWordLibrary
• 1.18: WordLibraries Facade
• 1.19: Find Usages
• 1.20: Exercise
• 1.21: Commiting Changes
• 1.22: GitHub Repository
• 1.23: Pushing Commits to Remote Repository on GitHub
• 1.24: Until Next Time
• 2.1: Welcome back
• 2.2: Setting up NetBeans Git Toolbar
• 2.3: Creating a Git Branch for Today's Session
• 2.4: Typical Directory Structure Under Maven
• 2.5: NetBeans Magic Shortcuts
• 2.6: Avoid Copy & Paste Programming
• 2.7: Creating a ShuffledWordLibrary
• 2.8: Integer Array for Shuffled Indexes
• 2.9: Finishing the methods to delegate to the other WordLibrary
• 2.10: Trying out the "ShuffledWordLibrary" That Does Not Really Shuffle
• 2.11: Committing Our Changes to Git
• 2.12: Shuffling the Integer Array
• 2.13: Trying Out the Shuffled Anagram List
• 2.14: Committing our "shuffle" method
• 2.15: ArrayShuffler
• 2.16: Creating an ArrayShufflerTest
• 2.17: Printing the indexes array
• 2.18: Fixing Random to be more random
• 2.19: Extending the Tests
• 2.20: The Goat, The Wolf and The Cabbage (Swapping Integer Values)
• 2.21: Testing the Integer Swapping Code
• 2.22: Testing Before Running Application
• 2.23: Fixing the Integer Swapping Code
• 2.24: Integer Swapping With XOR
• 2.25: Value of Source Control Systems
• 2.26: Changed WordLibrary from an Abstract Class to an Interface
• 2.27: Commit and Push
• 2.28: Until Next Time
• 3.1: Welcome back
• 3.2: Create a new Git Branch
• 3.3: ScrambledWordLibrary
• 3.4: SortedScrambledWordLibrary
• 3.5: Committing Entire Project At Once
• 3.6: Creating a RandomScrambledWordLibrary
• 3.7: Adding a shuffle(char[]) method
• 3.8: Testing the shuffle() method
• 3.9: Scrambler Strategy Extracted
• 3.10: Rot13Scrambler
• 3.11: OriginalScrambler
• 3.12: Moving Scrambler Interface Into ScrambledWordLibary Using IntelliJ IDEA
• 3.13: Moving Shuffler Implementations Into ScrambledWordLibrary
• 3.14: Danger of Overusing Inner Classer
• 3.15: Testing Refactoring
• 3.16: Beauty of IDE Interoperability
• 3.17: Anonymous Inner Classes
• 3.18: Converting Anonymous Inner Class to Lambda
• 3.19: Expression Lambdas
• 3.20: Font Ligatures
• 3.21: Testing and Commiting Lambdas
• 3.22: Turning Rot13Scrambler into a Lambda
• 3.23: Method References
• 3.24: Making ArrayShuffler.shuffle() Methods static
• 3.25: Forcing Everyone To Use Static Methods
• 3.26: DecoratedWordLibrary
• 3.27: ScrambledWordLibrary as a Decorator
• 3.28: ShuffledWordLibrary as a Decorator
• 3.29: Cleaning Up the Concrete Decorators
• 3.30: Updated Copyright Notices
• 3.31: Make Classes Final Where Possible
• 3.32: Commit and Push
• 3.33: Conclusion

We hope you enjoyed this tutorial. If you did, you will also enjoy our courses. We suggest you start with Extreme Java - Advanced Java, followed by Extreme Java - Concurrency Performance for Java 8.