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Java → Scala / Scala → Java

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Say you want to use the ProcessBuilder class from Java and its command function. From the Java doc:

ProcessBuilder(List<String> command)
    This constructs a process builder with the specified operating system program and arguments.

    List<String> command()
        This method returns this process builder's operating system program and arguments.

As can be seen, the constructor needs a List of Strings. However, in Scala we'd like to use an ArrayBuffer[String] and thus we have all the extra methods. Similarly, the command() returns a List of Strings, but it'd be awesome to get its result as an ArrayBuffer[String]. No problem, Scala can do implicit conversion for us.

import scala.collection.JavaConversions.bufferAsJavaList    // buffer TO Java List
import scala.collection.mutable.ArrayBuffer
val cmd = ArrayBuffer("ls", "-al", "/tmp")                  // create your buffer
val pb = new ProcessBuilder(cmd)                            // automatically converted to Java List

Let's see the other direction, i.e. converting a Java List to a Buffer:

import scala.collection.JavaConversions.asScalaBuffer       // (Java List) TO Scala Buffer
import scala.collection.mutable.Buffer
val b: Buffer[String] = pb.command()                        // Can't use ArrayBuffer!
                                                            // the wrapped object is only guaranteed to be a Buffer

// b: scala.collection.mutable.Buffer[String] = ArrayBuffer(ls, -al, /tmp)