PMD is a source code analyzer. It finds common programming flaws like unused variables, empty catch blocks, unnecessary object creation, and so forth. It supports Java, JavaScript, Salesforce.com Apex, PLSQL, Apache Velocity, XML, XSL.

Additionally it includes CPD, the copy-paste-detector. CPD finds duplicated code in Java, C, C++, C#, Groovy, PHP, Ruby, Fortran, JavaScript, PLSQL, Apache Velocity, Scala, Objective C, Matlab, Python, Go, Swift and Salesforce.com Apex.

In the modern era, software is commonly delivered as a service: called web apps, or software-as-a-service. The twelve-factor app is a methodology for building software-as-a-service apps that:

* Use declarative formats for setup automation, to minimize time and cost for new developers joining the project;
* Have a clean contract with the underlying operating system, offering maximum portability between execution environments;
* Are suitable for deployment on modern cloud platforms, obviating the need for servers and systems administration;
* Minimize divergence between development and production, enabling continuous deployment for maximum agility;
* And can scale up without significant changes to tooling, architecture, or development practices.

The twelve-factor methodology can be applied to apps written in any programming language, and which use any combination of backing services (database, queue, memory cache, etc).

Very good article describing the issues of having global state entities in software development.