[Scala 文章收集] How to create multiple class constructors in Scala

Source From Here 
Question 
Scala constructors FAQ: How do I create a Scala class with multiple constructors (secondary constructors)? 

How-To 
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: 

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1. package demo  
2.   
3. object Main extends App {  
4.   /**  
5.         * The main/primary constructor is defined when you define your class.  
6.       */    
7.   class Person(val firstName: String, val lastName: String, val age: Int) {    
8.     println("***Main Constructor***")  
9.       
10.     /**  
11.       * A secondary constructor.  
12.       */    
13.     def this(firstName: String) {    
14.       this(firstName, "", 0);    
15.       println("No last name or age given.")    
16.     }    
17.       
18.     /**  
19.         * Another secondary constructor.  
20.         */    
21.     def this(firstName: String, lastName: String) {    
22.       this(firstName, lastName, 0);    
23.       println("No age given.")    
24.     }    
25.       
26.     override def toString: String = {    
27.       return "%s %s, age %d".format(firstName, lastName, age)    
28.     }  
29.   }  
30.     
31.   // (1) use the primary constructor    
32.     val al = new Person("Alvin", "Alexander", 20)    
33.     println(al)    
34.     
35.     // (2) use a secondary constructor    
36.     val fred = new Person("Fred", "Flinstone")    
37.     println(fred)    
38.     
39.     // (3) use a secondary constructor    
40.     val barney = new Person("Barney")    
41.     println(barney)    
42. }  

If you run this example program as is, you'll get the following output: 

***Main Constructor***
Alvin Alexander, age 20
***Main Constructor***
No age given.
Fred Flinstone, age 0
***Main Constructor***
No last name or age given.
Barney , age 0

Supplement 
* [Scala IA] The Basics : Ch3. OOP in Scala - Classes and constructors