Variables and their types

A variable holds a value under a name. Every Java variable also has a type, which says what kind of value it can hold. Four types cover most of what you'll need for now:

A variable is created by writing its type, its name and its first value:

int apples = 12;
double price = 0.45;
boolean inStock = true;
String fruit = "apple";
System.out.println(fruit + ": " + apples + " at " + price);
System.out.println("In stock: " + inStock);

apple: 12 at 0.45
In stock: true

As the last two lines show, + joins numbers and booleans into text too: "In stock: " + inStock becomes In stock: true.

The type decides what fits

A variable can only hold values that fit its type. Putting a decimal number into an int would lose the part after the point, so Java refuses to compile it:

public class Main {
    public static void main(String[] args) {
        int price = 4.99;
        System.out.println(price);
    }
}

Main.java:3: error: incompatible types: possible lossy conversion from double to int
        int price = 4.99;
                    ^
1 error

The other way round is fine: double distance = 5; compiles, because a whole number fits in a double without losing anything (it becomes 5.0).

Note the capital S in String: it's a class, like Scanner, while int, double and boolean are built into the language and written in lower case.