I found the following three search engines that are specially designed for searching program source code. They will only index and search high quality source code with every line of code literally validated. My initial observations are that Codase is the best and JExamples.com searches only open source code written in Java.

• Codase - Source Code Search Engine
• Koders - Source Code Search Engine
• JExamples.com - Search Java Examples in Open Source Code
• Codefetch

About Codase

Codase is the leading source code search company with advanced source code understanding and xml index/search technologies. Rather than treating code as text, Codase understands programming languages, and treats code as code, the way it’s supposed to be. This unique and syntax-aware approach provides the most accurate and detailed search results with fine granularity levels of controls. With Codase, one can search functions, classes, strings, constants, macros, comments and other programming language constructs.

About Koders

Koders.com is the leading search engine for open source code. Our source code optimized search engine provides developers with an easy-to-use interface to search for source code examples and discover new open source projects which can be leveraged in their applications.

About JExamples.com

We analyze the source code of production Java open source projects such as Ant, Tomcat and Batik and load that analysis into a java examples database designed for easy searching. You enter the name of a Java API Class you want to see example invocations of and click Search.

About Codefetch, Inc

Codefetch’s mission is to connect programmers and authors so that programmers get the information they need, and the work of authors is supported and encouraged.