Primitive types

Java has eight primitive types — the simplest types, whose values are stored directly in the variable. All other data is built from them. The type determines how much memory a value takes and which numbers fit into it.

Whole numbers

There are four whole-number types of different sizes. int is used most often, and long for very large values:

void main() {
    int population = 146_000_000;
    long distance = 9_460_730_472_580L;
    IO.println(population);
    IO.println(distance);
}

Output:

146000000
9460730472580

Underscores make a number easier to read and change nothing. The L at the end says the number is a long.

Fractional numbers

Numbers with a fractional part use double or float. Usually you pick double: it is more precise. A float value is marked with the letter f:

void main() {
    double pi = 3.14159;
    float rate = 0.5f;
    IO.println(pi * 2);
    IO.println(rate);
}

Output:

6.28318
0.5

Characters

The char type holds a single character. It is written in single quotes, unlike a string in double quotes:

void main() {
    char grade = 'A';
    char letter = 'Ж';
    IO.println(grade);
    IO.println(letter);
}

Output:

A
Ж

char covers any Unicode character, not just Latin letters.

The boolean type

The boolean type has only two values: true and false. Such values come from comparisons and control conditions:

void main() {
    boolean isAdult = 20 >= 18;
    IO.println(isAdult);
}

Output:

true

Overflow

If a result does not fit into the type, it "wraps around" to the other end of the range. Java does not report an error:

void main() {
    int max = Integer.MAX_VALUE;
    IO.println(max);
    IO.println(max + 1);
}

Output:

2147483647
-2147483648

Integer.MAX_VALUE is the largest int value. If your numbers can get that large, use long.

Common mistake

A whole number written in code is an int by default. If it is outside the int range, the program does not compile — even when the variable is a long:

void main() {
    long big = 3000000000;
    IO.println(big);
}

Output:

Main.java:2: error: integer number too large
    long big = 3000000000;
               ^
1 error
error: compilation failed

Add the letter L: 3000000000L.