Scala中Runnable的return、异常处理及方法定义相关技术疑问

Hey there! Let's walk through each of your questions about your Scala MyProg class (which extends StrictLogging and Runnable) clearly:

1. Is using return inside the process() method of a Runnable reasonable? And is my understanding correct that even if I return midway, process() will still be called periodically based on intervalSeconds? #

First off, using return in a Unit-returning method like process() is syntactically valid in Scala. Since the method returns Unit, you’d typically use return without a value (or return ()), and it just terminates the current invocation of process() early.

Your understanding about the periodic calls is spot-on. The return only exits the current invocation of process()—it doesn’t interfere with the underlying scheduler that triggers the method at each intervalSeconds interval. As long as the scheduler’s thread is still running, process() will keep getting called on schedule, even if you bail out early with return in some runs.

2. Can I call System.exit(0) or throw an exception here? Will process() be called again after these operations? #

Let’s break this down into two scenarios:

• Calling System.exit(0): You absolutely can do this, but keep in mind that System.exit() terminates the entire JVM process immediately. Once that happens, there’s no way for process() (or any other code in your app) to run again—everything stops cold.
• Throwing an exception: Whether process() gets called again depends on how your scheduler handles uncaught exceptions. For example, if you’re using Java’s ScheduledExecutorService (a common choice for periodic tasks), if your process() throws an uncaught checked or unchecked exception, the scheduler will stop scheduling future invocations of that task. If you’ve wrapped the process() call in a try/catch block (either inside the method or in the scheduler’s task wrapper) that handles the exception, then the scheduler will continue triggering process() at the next interval.

3. Why is the process() method defined as def process() :Unit {}, and can I switch to def process() :Unit = {}? #

In Scala, these two syntaxes are semantically equivalent for Unit-returning methods. The def process(): Unit {} style is an older, more Java-like syntax where the compiler infers that the method returns Unit because there’s no = sign and the body is a block of statements.

You absolutely can switch to def process(): Unit = {}—in fact, this is the preferred style in modern Scala. Using the = makes the method definition more consistent with Scala’s functional programming paradigm, and it’s clearer that you’re explicitly defining the method’s return behavior. If you ever decide to change the method’s return type later, you won’t have to adjust the syntax structure (you’d just replace Unit with the new type), which makes the code more maintainable.

内容的提问来源于stack exchange，提问作者BAE