Round to One Decimal Place in Java

Instructor: David Gloag

David has over 40 years of industry experience in software development and information technology and a bachelor of computer science

In this lesson, we'll take a look at rounding in Java, specifically how you can round to one decimal place. At the end, you should have a good understanding of these important tools and techniques.

To Calculate or Not

Calculation, fun and easy for some, a nightmare for others. Most of us can remember our grade school days and the numerous math classes we took. There was a purpose to it, of course, to teach us basic math skills. For the younger generations, life is a little different. They have grown up with calculators and computers, devices that can perform calculations for them. But, how accurate do we need to be in our calculations? For example, do we need the constant π calculated to ten decimal places? In most cases no, two are usually enough. So, we've developed ways to round these constants in computer calculations using tools like Java.

What is Java?

Java is a general-purpose computer programming language. It is high-level, meaning that it has a one-to-many conversion rate to the machine language code it generates. And like most programming languages, it has the ability to perform calculations, things like adding, subtracting, multiplication, and division. It also has the ability to vary the accuracy of reporting those calculations.

What is Rounding?

Rounding is a process we use to control the accuracy of a value we generate. Accuracy is a term for that reflects how close the value is to an actual, known value. Consider for a moment the constant π mentioned above. If you look it up on Google, you will find the value 3.14159. We know π is an irrational number that this is non-terminating and non-repeating, so this value is an estimate. It is not completely accurate, but for most purposes, it will do just fine. Rounding is a similar idea, but it adds some rigor to the creation process. As an example, let's look at π rounded in various ways:

  • To One Decimal Place - 3.1
  • To Two Decimal Places - 3.14
  • To Three Decimal Places - 3.142
  • To Four Decimal Places - 3.1416

Can you see the pattern? To round to a specific decimal place, you look at the next value. If it is five or greater, you add one to the value of that decimal place. If it's four or lower, you leave it as is. The process is that simple. Also, note that you can only round to the nth decimal place if a value exists for the n+1th decimal place.

Rounding to One Decimal Place in Java

Because rounding is used quite often, most programming languages provide a number of ways to accomplish this task. Java is no different. Common methods include:

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