Scala: Packages

Scala packages are similar to Java packages with few differences.

 

In Scala,

a.   a single source file have contributions to multiple packages.

b.   No relationship between packages and source directories.

 

Step 1: Create new Scala project ‘packages-demo’ in Eclipse.

 

Step 2: Create new scala package object ‘com.sample.app.model’.

 

Define new Scala class Employee.scala in the package ‘com.sample.app.model’.

 

Employee.scala

package com.sample.app.model

class Employee(id: Int, firstName: String, lastName: String) {
  
  override def toString = s"$id : ($firstName, $lastName)"
  
}

 

Step 3: Define Scala App class MainApp in the package ‘com.sample.app’.

 

MainApp.scala

 

package com.sample.app

import com.sample.app.model.Employee

object MainApp extends App {
  
  val emp1 = new Employee(1, "Ram", "Gurram")
  
  println(emp1)
  
}

Total project structure looks like below.

 

Run MainApp.scala, file, you will see below messages in console.

 

1 : (Ram, Gurram)

 

import com.sample.app.model.Employee

To use Employee class in current Scala application, you should import it.

 

How to import all the classes of a package?

Use package._ to import all the types of package.

 

Example

import com.sample.app.model._

 

How static imports work?

It is similar to normal imports.

 

import java.util.Math._

 

Above statement imports all the static methods of Math class.

 

You can download complete application from below link.

https://github.com/harikrishna553/scala-examples/tree/master/packages-demo

 

Single source file have contributions to multiple packages.

In Scala, you can define types that belongs to multiple packages in same source file.

 

AppModels.scala

package com.sample.app

package com {
  package sample {
    package app {

      package dao {
        class User(id: Int, name: String) {
          override def toString = s"$id : ($name)"
        }
      }

      package dto {
        class UserDto(id: Int, name: String) {
          override def toString = s"$id : ($name)"
        }
      }

    }
  }
}

MainApp.scala

package com.sample.app

import com.sample.app.dao.User
import com.sample.app.dto.UserDto

object MainApp extends App {

  val user1 = new User(1, "Ram")

  val userDto1 = new UserDto(1, "Ram")

  println(user1)

  println(userDto1)

}

 

Run MainApp.scala file, you will see below messages in console.

 

1 : (Ram)

1 : (Ram)

 

https://github.com/harikrishna553/scala-examples/tree/master/nested-packages

 

Note

a. How to import more than one class of a package?

Import java.util.{List, Map}

 

If you are comfortable with multi line imports you can use this.

 

Import java.util.List

Import java.util.Map

 

b. Create alias of a class

import java.util.{ArrayList => MyArrayList}

 

Aliases are used to resolve name conflicts of types.

 

c. Import everything from a package except this type

import java.util.{ArrayList => _, _}

Above statement import all the types except ArrayList.

 

d. imports can be used anywhere, not necessarily at top of the file.

package com.sample.app

object MainApp extends App {

  import java.util.Arrays

  var myList = Arrays.asList(2, 3, 5)

  myList.forEach(println)
}

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