Skip to content

Category: Java Basics

Exception handling in ScheduledExecutorService

Java’s ScheduledExecutorService allows you to schedule Runnable tasks without having to worry too much about creating Threads. At its simplest, you can schedule a task like this:

Runnable task = () -> System.out.println("Hello world!");
executor.schedule(task, 10, TimeUnit.SECONDS);

The output is:

Hello world!

That is we schedule the task, then print “Done!”. 10 seconds later the scheduled task executes and prints “Hello world!”.

But what happens if the Runnable throws an Exception?

Execute Around idiom in Java

The Execute Around idiom is a pattern that allows you to wrap an action with some standard setup / tear down steps. Examples might include:

  • Execute within a lock: acquire the lock, do the action, release the lock
  • Resource handling: acquire the resource, do the action, close the resource
  • Execute as a user: switch to the user, do the action, switch back to the original user
  • Exception handling: do the action, handle the exceptions
  • Time an action: start a timer, do the action, stop the timer

The pattern allows you to pass in arbitrary actions and have them run with the same setup / tear down steps.

Testing for SimpleDateFormat thread safety

It’s a little alarming how many good developers are unaware that many standard Java classes – including subclasses of Format – are not thread safe. Many are also not sure about how their applications perform in a multi-threaded environment or how their web application container (Tomcat) will run their app in multiple threads. This can cause nasty intermittent bugs that can be incredibly hard to find and fix. It’s important to be aware of threading issues at development time but it’s also important to be able to test for them.

Currency and BigDecimal

I’m studying for SCJP – currently tackling a rather dull section on regular expressions. I’ve just noticed that the exam does not cover BigDecimal. I really don’t understand this. BigDecimal is essential for any fixed precision decimal representation and calculation. Put another way: if you’re not aware of BigDecimal, you can’t effectively represent money in your program. Surely more useful than awareness of the \w, \s and \d regex metacharacters, no?

Bean introspection

Spotted this nasty little quirk today – not for the first time. Every time I see it I want to get angry at someone but I’m not quite sure who.

What’s wrong with this list of properties?

private String name;
private String address;
private String eMail;

Nothing immediately obvious perhaps. Here are the standard generated getters and setters (signatures only):

public String getName();
public void setName(String name);

public String getAddress();
public void setAddress(String address);

public String getEMail();
public void setEMail(String eMail);

All perfectly valid. Now, given these auto-generated getters and setters, what names would standard bean introspection derive?


Hang on, what happened there? How did my eMail property turn into EMail?