Java is an object-oriented language.

• http://www.java.sun.com/

Compilers

• Java Decompilers
• Java Dynamic Compilers
• Java Native Compilers

Transformation Systems

• Java Parser Generators
• Transformation systems for Java operate on an abstract syntax representation of Java source code. Unfortunately there are no standard structures for the abstract syntax of Java. See Java Abstract Syntax for the available implementations.
• Java Concrete Syntax definitions

• Sun's Annotation Processing Tool for generating or analysing code at compile-time based on annotations.
• Stratego/XT with Java Front
• DMS Software Reengineering Toolkit

• Compost Framework
• JJTraveler -- visitor combinator framework for Java
• JTOM -- pattern matching compiler

Analysis and Searching

• JQuery -- query-based source code browser based on Eclipse

Bytecode

• Soot Framework for bytecode transformations (Jimple)
• Apache's BCEL
• ASM

Extensible Compilers

• Polyglot Extensible Compiler Framework
• AspectBench Compiler (abc) for AspectJ
• OpenJava

Code Generation

• Meta-AspectJ
• Jakarta Tool Suite (JTS), especially the Jak language

Publications

Tools and methods for Java Program Understanding and Reverse Engineering are discussed in several of the papers by Tarja Systa.

• Tarja Systä, Kai Koskimies, and HausiMueller. Shimba - An Environment for Reverse Engineering Java Software Systems, Software Practice and Experience, 31(4), 2001, pp. 371-394.
• Tarja Systä, Understanding the Behavior of Java Programs, In Proc. of the 7th Working Conference on Reverse Engineering (WCRE 2000), Brisbane
• Tarja Systä, On the relationships between static and dynamic models in reverse engineering Java software, In Proc. of the 6th Working Conference on Reverse Engineering (WCRE99), Atlanta, Georgia, USA, October 1999, pp.304-313.
• See http://www.cs.tut.fi/~tsysta/