2009-01-22

Design Pattern : Good Citizen

Imagine a software system where there is no need for you to spend your time programming defensively; your objects will be used responsibly, and your methods will always be passed sensible arguments. This low-friction utopia can be approached by establishing some simple programming rules so that every class acts as a 'good citizen' in the society of classes collaborating at runtime. This page outlines some rules that we, and others, believe lead to good citizenship. All are aimed at improving clarity, reducing surprise, and promoting basic consistency. As a good citizen, I...
  • Keep a consistent state at all times - init() or populate() is a code smell.
  • Have no static fields or methods
  • Never expect or return null.
  • Fail fast - even when constructing.
  • Am Easy to test- all dependent object I use can be passed to me, often in my constructor (typically as Mock Objects).
  • Accept dependent object that can easily be substituted with Mock Objects (I don't use Concrete Class Dependency).
  • Chain multiple constructors to a common place (using this(...)).
  • Always define hashCode() alongside equals()
  • Prefer immutable value objects that I can easily throw away.
  • Have a special value for 'nothing' - e.g. Collections.EMPTY_SET.
  • Raise checked exceptions when the caller asked for something unreasonable - e.g. open a non-existant file.
  • Raise unchecked exceptions when I can't do something reasonable that the caller asked of me - e.g. disk error when reading from an opened file.
  • Only catch exceptions that can be handled fully.
  • Only log information that someone needs to see.
© Dan North, Aslak Hellesoy; found at PicoContainer Design Patterns

2009-01-19

Changing Windows XP HAL

If you perform a Windows installation with default settings in VirtualBox, Halacpi.dll will be chosen as VirtualBox enables ACPI by default but disables the IO APIC by default. A standard installation on a modern physical PC or VMware will usually result in Halaacpi.dll being chosen as most systems nowadays have an IO APIC and VMware chose to virtualize it by default (VirtualBox disables the IO APIC because it is more expensive to virtualize than a standard PIC). So as a first step, you either have to enable IO APIC support in VirtualBox or replace the HAL. Replacing the HAL can be done by booting the VM from the Windows CD and performing a repair installation.
© VirtualBox Wiki; Migrate Windows

2009-01-09

Java Performance Benchmarks

Several benchmarks comparing C++ and Java exist on the web. The results are mixed: some show that Java is actually faster than C++, while most show that C++ is still faster than Java but by a small margin. The purpose of this post is to talk about the theory behind the Java optimization techniques, so I didn't set out to create my own benchmarks myself, but nothing like hard data to prove a point. So here are the links to some benchmarks found on the web:
  • The Java is Faster than C++ and C++ Sucks Unbiased Benchmark: despite the name, this benchmark shows very similar results between Java and C++, with the occasional scenario where C++ beats Java hands down.
  • The Java Faster than C++' Benchmark Revisited: someone who didn't like the benchmark above and found different results, where C++ has a clearer lead. Even so, Java is still close, wins some benchmarks, and is clearly slow only in a handful of tests.
  • The Computer Language Benchmarks Game: compares a number of programming languages using different algorithms. Gnu C++ and Java 6 are compared, and C++ wins most of the comparisons, but in most of the cases by a very close margin, and Java is the occasional winner in some of the tests.
© Domingos Neto; Java Performance
...and one more update: Stefan Krause; Update for Java Benchmark.