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Scala constructors FAQ: How do I create a Scala class with multiple constructors (secondary constructors)?
The Scala approach to defining multiple class constructors is a little different than Java, but somewhat similar. Rather than try to explain this in words, I just created some example source code to demonstrate how this works.
Here's some source code to demonstrate the Scala "multiple constructors" approach:
package tests
object MultipleConstructors {
def main(args: Array[String]) {
// (1) use the primary constructor
val al = new Person("Alvin", "Alexander", 20)
println(al)
// (2) use a secondary constructor
val fred = new Person("Fred", "Flinstone")
println(fred)
// (3) use a secondary constructor
val barney = new Person("Barney")
println(barney)
}
}
/**
* The main/primary constructor is defined when you define your class.
*/
class Person(val firstName: String, val lastName: String, val age: Int) {
/**
* A secondary constructor.
*/
def this(firstName: String) {
this(firstName, "", 0);
println("\nNo last name or age given.")
}
/**
* Another secondary constructor.
*/
def this(firstName: String, lastName: String) {
this(firstName, lastName, 0);
println("\nNo age given.")
}
override def toString: String = {
return "%s %s, age %d".format(firstName, lastName, age)
}
}
If you run this example program as is, you'll get the following output:
Alvin Alexander, age 20 No age given. Fred Flinstone, age 0 No last name or age given. Barney , age 0
I'm not going to write any more about the Scala constructors approach today, but if you have any questions, comments, or corrections about this example, just leave a note in the Comments section below.
