Data Types in Java

What are data types

A data type tells Java what kind of value a variable holds — a whole number, a decimal, a character, true/false, or text. Java is strongly typed, so every variable has a type. Java's types fall into two groups: primitive types and reference types.

Primitive vs reference

Primitive types store the actual value in the variable — fast and simple. There are exactly eight. Reference types (String, arrays, objects) store a reference that points to data elsewhere in memory. Understanding this split explains a lot of Java behaviour later.

Integer types

int  count = 100;
long big   = 10000000000L;   // L marks a long

int is the everyday choice for whole numbers. Use long for very big values, with an L suffix.

Decimal types

float  temp  = 36.6f;   // f marks a float
double price = 99.99;   // default for decimals

double is the default and most precise choice for decimals. float uses less memory but is less precise, and needs an f suffix.

char and boolean

char    grade = 'A';    // one character, single quotes
boolean pass  = true;   // only true or false

char holds a single character in single quotes. boolean holds only true or false — perfect for conditions and yes/no flags.

Reference types

String name = "Aman";           // text (a class)
int[]  marks = {90, 85, 78};    // an array

System.out.println(name.length());   // 4

String and arrays are reference types — they point to objects. That is why String is capitalised and comes with methods like length(). Primitives have no methods.

Common mistakes

• Overflowing int. Very large numbers need long with an L suffix.
• Forgetting the f on float. float x = 1.5; errors — write 1.5f.
• Using double quotes for char. char uses single quotes: 'A', not "A".
• Thinking String is primitive. It is a class (reference type), written with a capital S.

Summary

• Data types define what kind of value a variable holds.
• Java has 8 primitive types and reference types like String and arrays.
• Whole numbers: byte, short, int, long; decimals: float, double.
• char is one character; boolean is true/false.
• Reference types point to objects and have methods; primitives do not.

Next, store values in Java variables, or work with them using Java operators.