Category Archives: Java

Object equality is context sensitive

Equality is context sensitive. It’s very rarely as cut-and-dried as people think it is.

As a simple example, consider two $5 notes. I think everyone can agree that these notes have the same value – they are both worth $5. But are they equal?

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Immutable objects the lazy way

Building properly immutable objects in Java can be annoying, especially if they’ve got a bunch of properties – too many to put into a readable constructor.1

You can implement the Builder pattern, but a lot of the time that just feels like overkill. But you don’t want to put in a bunch of setter methods, because that’s just asking for trouble. So what do you do?

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Java, Equality, Mutability

TL;DR version: Don’t implement equals() on mutable objects.

This is a post I’ve been tossing around for a couple of years, ever since a lunchtime debate with a colleague. It’s a simple statement: You shouldn’t implement the equals() method if your object isn’t immutable.1

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Example Hadoop Job that reads a cache file loaded from S3

I had all sorts of problems getting my head around how cache files work with Hadoop. Finally, I stumbled across the answer – when you add a cache file (see HadoopMain#48), it’s available to read as a local file inside the mapper (MyMapper#36).

When running in Elastic MapReduce, the file URI can be an S3 file, using either s3://bucket/path or s3n://bucket/path – this may or may not work in other Hadoop implementations, but the general approach would work fine.

See the gist at https://gist.github.com/twasink/8813628

How-To: Grails, GORM and SimpleDB

I went to build a new Grails-based app today, and I wanted to use SimpleDB as a backend (the app is an internal-use administration app, to configure a suite of AWS-deployed apps). So I went looking on how to use GORM with SimpleDB. This turned out to be a non-trivial task, so I thought I’d share the process with everyone.

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Building Dependent Maven Projects in Bamboo

For the last year or so, I’ve been using Atlassian’s Bamboo (in the OnDemand variant) for our team’s build server. And, mostly, it’s an awesome tool. Some parts, however, are a little rough around the edges. Building dependent projects is one of them.

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