Everything in a Java program works with data—numbers, characters, text, true/false flags, dates, and more. To work with these effectively, Java provides a rich set of data types, broadly grouped into primitive types and object-based types.

Primitive types are the most basic building blocks of data in Java. They’re efficient, fixed in size, and not objects.

Used for whole numbers. Example:

int age = 25;

Used for decimal numbers. Example:

double price = 19.99;

Used for true/false values. Example:

boolean isActive = true;

Used to represent a single character. Example:

char grade = 'A';

Other primitive types include:

• byte – very small integers (-128 to 127)
• short – small integers
• long – very large integers
• float – less precise decimals

You’ll usually start with int, double, and boolean for most cases.

Java is an object-oriented language, so it also supports types that are full-fledged objects. These types provide additional behavior and methods.

Used for text data. Example:

String name = "Alice";

Strings come with many useful methods like length(), toUpperCase(), etc. We’ll explore Strings in detail in the upcoming chapters.

Used to work with dates and times. Example:

LocalDate today = LocalDate.now();

Handling dates and times properly is important and deserves its own space—we’ll see this in a later chapter.

Java automatically converts between primitive types and their object counterparts when needed. This is known as autoboxing and unboxing.

Example:

Integer count = 10; // int to Integer (autoboxing)
int x = count;      // Integer to int (unboxing)

Each primitive has a corresponding wrapper class:

• int → Integer
• double → Double
• boolean → Boolean, etc.

Java gives you the right type for every kind of data—whether it’s raw performance with primitives or richer behavior with object-based types. Mastering data types early on will make your code more reliable, readable, and efficient.