Why does this code, written backwards, print “Hello World!”

Question

Here is some code that I found on the Internet:

class M‮{public static void main(String[]a‭){System.out.print(new char[]
{\'H\',\'e\',\'l\',\'l\',\'o\',\' \'         


        

Answer 1

The Character U+202E mirrors the code from right to left, it is very clever though. Is hidden starting in the M,

"class M\u202E{..."

How did I found the magic behind this?

Well, at first when I saw the question I tough, "it's a kind of joke, to lose somebody else time", but then, I opened my IDE ("IntelliJ"), create a class, and past the code... and it compiled!!! So, I took a better look and saw that the "public static void" was backward, so I went there with the cursor, and erase a few chars... And what happens? The chars started erasing backward, so, I thought mmm.... rare... I have to execute it... So I proceed to execute the program, but first I needed to save it... and that was when I found it!. I couldn't save the file because my IDE said that there was a different encoding for some char, and point me where was it, So I start a research in Google for special chars that could do the job, and that's it :)

A little about

the Unicode Bidirectional Algorithm, and U+202E involved, a briefly explain:

The Unicode Standard prescribes a memory representation order known as logical order. When text is presented in horizontal lines, most scripts display characters from left to right. However, there are several scripts (such as Arabic or Hebrew) where the natural ordering of horizontal text in display is from right to left. If all of the text has a uniform horizontal direction, then the ordering of the display text is unambiguous.

However, because these right-to-left scripts use digits that are written from left to right, the text is actually bi-directional: a mixture of right-to-left and left-to-right text. In addition to digits, embedded words from English and other scripts are also written from left to right, also producing bidirectional text. Without a clear specification, ambiguities can arise in determining the ordering of the displayed characters when the horizontal direction of the text is not uniform.

This annex describes the algorithm used to determine the directionality for bidirectional Unicode text. The algorithm extends the implicit model currently employed by a number of existing implementations and adds explicit formatting characters for special circumstances. In most cases, there is no need to include additional information with the text to obtain correct display ordering.

However, in the case of bidirectional text, there are circumstances where an implicit bidirectional ordering is not sufficient to produce comprehensible text. To deal with these cases, a minimal set of directional formatting characters is defined to control the ordering of characters when rendered. This allows exact control of the display ordering for legible interchange and ensures that plain text used for simple items like filenames or labels can always be correctly ordered for display.

Why create some algorithm like this?

the bidi algorithm can render a sequence of Arabic or Hebrew characters one after the other from right to left.