Question

Is there an implicit method to convert scala.collection.mutable.StringBuilder to java.lang.StringBuilder?

I am using a Java library (JCommander) in which one of the methods (usage) takes a java.jang.StringBuilder argument.

Answer 1

You can’t start with a Scala StringBuilder and then obtain the Java version. You can, however, wrap a java.lang.StringBuilder in the Scala version. So:

val jsb = new java.lang.StringBuilder();
val sb = new StringBuilder(jsb);
// Do Scala-y stuff with sb
JCommander.whatever.usage(jsb);
// Do more Scala-y stuff

Since–not a guarantee, but true in practice right now (2.8, 2.9)–the Scala wrapper doesn’t store any state (instead just referring to the Java version), you’re safe to mix and match usage of the two.