Java uses packages to organize classes. Kotlin also has packages and they work in the same way. The biggest difference from Java is that declaring a package is optional. In Kotlin you can have a file or a class without a package.

Package declaration has to be at the top of the file. If you want to use other types that are declared in the same package, then you can access them directly. If they are declared in another package, then you have to import them first. The following example shows a package and import declarations. It shows how a package is declared on the top, uses an import from the Java standard library and declares a function on a file level:

package quickstartguide.kotlin.chapter2

import java.lang.Math.PI

fun circumference(radius: Double): Double {
    return 2 * PI * radius
}

Unlike Java, where you import classes, Kotlin allows importing of any kind of declarations.

If you were to import the circumference function from the preceding example, it would look like this:

import quickstartguide.kotlin.chapter2.circumference

val circ = circumference(10.0)

You can also import every declaration from a package with the wildcard imports. If you were to declare this inside a file, this is what you would use:

import java.util.*

You’d have access to every declaration inside the java.util package.