http://stackoverflow.com/questions/609744/what-is-the-rationale-behind-having-companion-objects-in-scala
這URL提到一件有趣的事：雖然Companion是用來存static的資訊，但是它本身實作並不是用Java static做到的。
還有另外一個重要的問題：為什麼要用Companion object?
目的是讓class的本名可以當factory用，才不會一堆AbcFactory到處亂噴……
-Shannon
From: trend_fp-bounce@xxxxxxxxxxxxx [mailto:trend_fp-bounce@xxxxxxxxxxxxx] On
Behalf Of ???
Sent: Friday, May 15, 2015 12:50 PM
To: trend_fp@xxxxxxxxxxxxx
Subject: [trend_fp] class and object的反組譯結果
Account.scala
class Account
{
var class_id = "1234567"
def print_account() = { println(Account.object_id)}
}
object Account
{
//def print_account() = { println(Account.class_id)} cannot access class
Account' s class_ud
var object_id = "7654321"
}
編譯之後生出兩個class
Account.class
import scala.Predef$;
public class Account
{
public static void object_id_$eq(String s)
{
Account$.MODULE$.object_id_$eq(s);
}
public static String object_id()
{
return Account$.MODULE$.object_id();
}
public String class_id()
{
return class_id;
}
public void class_id_$eq(String x$1)
{
class_id = x$1;
}
public void print_account()
{
Predef$.MODULE$.println(Account$.MODULE$.object_id());
}
public Account()
{
class_id = "1234567";
}
private String class_id;
}
Account$.class -> object Account
public final class Account$
{
public String object_id()
{
return object_id;
}
public void object_id_$eq(String x$1)
{
object_id = x$1;
}
private Account$()
{
object_id = "7654321";
}
public static final Account$ MODULE$ = this;
private String object_id;
static
{
new Account$();
}
}
Mike
--
方鍾豪 (Mike Fang)
Pervasive Embedded Technology Lab
Department of Computer Science, National Chiao Tung University
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