Java: Magic Numbers

Recall one of the past lessons:

var euros = 1000;
var dollars = euros * 1.25; // => 1250
var rubles = dollars * 60; // => 75000


From the point of view of professional development, this code "smells." This is how code that does not correspond to the so-called best practices is described. And the reason is this: right now, looking at the numbers 60 and 1.25, you are most likely wondering: "What are these numbers?". And imagine what will happen in a month! And how will a new programmer understand him, who has not seen the code before? In our example, the context is restored due to proper naming, but in real life the code is much more complicated, and therefore it is often impossible to guess the meaning of numbers.

This “smell” is called magic numbers. Numbers whose origin is impossible to understand without a deep knowledge of what is happening inside this part of the code.

The way out is simple: it is enough to create variables with the correct names, how everything will fall into place.

var dollarsInEuro = 1.25;
var roublesInDollar = 60;

var euros = 1000;
var dollars = euros * dollarsInEuro; // => 1250
var rubles = dollars * roublesInDollar; // => 75000


Pay attention to the following details:

  • Naming lowerCamelCase
  • Two new variables are separated from subsequent calculations by a blank line. These variables make sense without computations, so this separation is appropriate, it improves readability.
  • It came out well-named and structured code, but it is longer than the previous version. This is often the case, and this is normal, because the code should be readable.


You are faced with this code, which displays the total number of rooms in the possession of the current king:

var king = "King Balon the 6th";
System.out.print(king + "has" + (6 * 17) + "rooms.");

As you can see, these are magic numbers: it is not clear what 6 is and what 17. It is possible to guess if you know the history of the royal family: each new king inherits all the castles from their ancestors and builds a new castle - an exact copy of the parent.

This strange dynasty just breeds the same castles ...

Get rid of the magic numbers by creating new variables, and then display the text.

It will turn out like this:

King Balon the 6th has 102 rooms.

Variable names should convey the meaning of numbers, but at the same time they should remain sufficiently short and capacious for comfortable reading.

Remember: the code will work with any names, and our system always checks only the result on the screen, so the execution of this task is under your responsibility.

If you got stuck and don't know what to do, you can ask a question in our huge and friendly community