One feature of Scala is it reuse Java's Exception class hierarchies, but much easier to use. For one thing, it treats Exception as "unchecked" just like RuntimeException, which I think one of the reason it causes Java to be unnecessary verbose. For example when opening a file stream, one way Java can do it is:

public void doFile(File file) throws FileNotFoundException, IOException {  
  FileInputStream fins = null;
try{
fins = new FileInputStream(file);
//process it.
}finally{
if(fins != null){ fins.close(); }
}
}

But in Scala equivalent can be done as follow:
def doFile(file: File): Unit = {  
  val fins = new FileInputStream(file)
try{
//process it.
}finally{
fins.close
}
}

In Scala, you don't need to predefine the "fins" to null then try it, and then check to close in finally block, because if FileInputStream failed, an FileNotFoundException instance will be thrown out of the method, before reaching to the try block. In addition, the Scala user of the doFile method do NOT need to invoke it inside a try/catch block, while Java requires it. This is possible because Exception, or any subclasses are "uncheck" as default in Scala. This mean that the exception will keep throw to next stack frame until it finds a "catcher". If none are found, it will exit main at the end.

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Happy 10th year, JCertif!

Notes

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Created by Michael Levin Dec 18, 2008 at 6:56pm. Last updated by Michael Levin May 4, 2018.

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