Data Types (Primitives & Ranges)

In the Variables lesson you met int, double, String and boolean. Now let's go deeper: Java's eight primitive types, exactly how much each one can hold, and how picking the right type prevents subtle bugs like overflow and rounding errors.

Learn Data Types (Primitives & Ranges) in our free Java course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick…

Part of the free Java course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

Java has exactly 8 primitive types . A primitive stores a raw value directly in a fixed block of memory — there is no object, no method, and it can never be null . They split into two families:

Each step is twice the bits, so twice the range.

double has roughly twice the precision of float.

The remaining two don't fit either family: char holds a single character, and boolean holds only true or false .

💡 Analogy: Think of types as buckets of different sizes. A byte is an egg cup, an int is a kitchen jug, and a long is a water barrel. You could carry a teaspoon of water in a barrel, but it wastes space — and you can't pour a barrel into an egg cup without spilling.

Because every primitive has a fixed size, its minimum and maximum values are constants baked into the language. Memorise the int range; look the rest up via the wrapper classes ( Integer.MAX_VALUE , Long.MIN_VALUE , etc.).

* The JVM doesn't truly use a single bit; size is implementation-defined. The "Default" column is the value a field gets when you don't initialise it (local variables get no default — you must assign them).

Because each type has a hard ceiling, going one past it doesn't throw an error — it silently wraps back to the minimum, like an odometer rolling over to zero.

A char looks like a letter, but internally it's an unsigned 16-bit number — the Unicode code point . That means you can do arithmetic on characters:

This trick — treating letters as numbers — is the basis of cipher puzzles, sorting, and case-conversion. Single quotes mean char ; double quotes mean String . They are not interchangeable.

You rarely need the exotic types. Use this decision guide:

These lines are scrambled. Put them in the correct order so the program declares a long file size, converts it to a double in megabytes, and prints it.

Why: The class and method headers must come first. bytes must be declared before it can be used, and it needs the L suffix because 5.3 billion overflows int . We divide by 1024.0 (a double) so the division is floating-point, not integer — giving 5120.00 MB .

-2147483648 . Adding 1 to the largest int overflows and wraps to the smallest int.

C . 'A' is 65, plus 2 is 67, and casting 67 back to char gives 'C' .

3 then 3.5 . The first is integer division (both ints, decimal dropped); the second has a double operand, so it's floating-point division.

You now know all 8 primitive types, their exact ranges, why long needs L and float needs f , how overflow silently wraps, and why double is wrong for money. Most of your code will use int , double , and boolean — but now you know what the others are for.

Next up: Type Casting — safely (and unsafely) converting values from one type to another.

Practice quiz

• Browse all free courses
• Cheat sheets & quizzes
• Coding dictionary