Java Fundamentals Prework Primitive Data Types

What is a data type?

5 min

In Java, data is stored in variables so that you can access and manipulate that data throughout our apps. Each variable has a data type associated with it, and the variable can only hold that type of data.

When you create variables, you must assign the variable a data type. The data type of that variable cannot be changed from that point.

🧠 These qualities mean that Java is designed to enforce type safety. People also describe Java as statically typed - meaning that once a variable is assigned a data type, the type cannot change.

Throughout this lesson, you’ll explore how data types and variables form the basic building blocks of programming a Java application and how you use them to store information in our programs.

Primitive data types in Java

10 min

In computer science and computer programming, a data type — or simply, type — is a classification identifying one of the various types of data that determines:

Data types are often similar across different languages, including English. Java has eight primitive data types, all described below. We’ll start with the most common, then briefly touch on some less common ones.

Category Data type Description Example
True or False boolean Represents either true or false. true, false
Integer int Whole numbers ranging from -2,147,483,648 to 2,147,483,647. -9000, 1024, 1_000_000
Floating-point double Positive or negative decimal numbers with about 16 digits of precision after the decimal. 3.14159265359, 1.0, 56D

By default, an integer literal will be of type int, and a floating-point literal will be of type double. You can also specify a number as a double by adding a d or D to the end of it.

Numeric literals can optionally include underscores to make large numbers easier to read. For example, the int 1_000_000 above will be interpreted as 1000000. The underscores purely make the literal more readable. There are a few rules for using this pattern. For example, never start or end a number with _.

The following primitives are less common but do have use cases:

Category Data type Description Example
Integer byte Whole numbers ranging from -128 to 127. 4, 8, 15, 16, 42
Integer short Whole numbers ranging from -32,768 to 32,767. -20, 9001, 16384
Integer long Whole numbers ranging from ~-9 quintillion to ~9 quintillion. 9_223_372_036_854_775_807L, 16L
Floating-point float Positive or negative decimal numbers with about 7 digits of precision after the decimal. 3.14159F, 1.0F, -80.80F
Character char A single character surrounded by single quotation marks. The building block of strings. 'a', 'A', '7', '@'

The byte, short, and float types can be useful in memory-constrained environments. Floating-point literals that end in an f or F will be of type float.

The long type can represent a larger range of numbers than the int data type. Integer literals that end in an l or L will be of type long. When implementing these, the capital L is preferred over l because of how similar l can look to the 1 digit.

The float type implements the single-precision 32-bit IEEE 754 floating point format standard, and the double type implements the double-precision 64-bit IEEE 754 floating point format standard.

The IEEE 754 standard is complex, and its intricacies are largely out of the scope of this lecture. That said, you will see some of those intricacies while exploring these data types more.

It is important to know that you should not use float or double data types to represent floating-point numbers where exact precision is required, such as currency calculations.

As you continue through this lesson we’ll elaborate on the types above and show you some helper methods to manipulate them.