CheckStyle
Checkstyle is a development tool to help programmers write Java code that adheres to a coding standard. It automates the process of checking Java code to spare humans of this boring (but important) task. This makes it ideal for projects that want to enforce a coding standard.

Classycle
Classycle's Analyser analyses the static class and package dependencies in Java applications or libraries. It is especially helpful for finding cyclic dependencies between classes or packages.

Condenser
Condenser is a tool for finding and removing duplicated Java code. Unlike tools that only locate duplicated code, the aim of Condenser is to also automatically remove duplicated code where it is safe to do so.

Dependency Finder
Dependency Finder is a suite of tools for analyzing compiled Java code. At the core is a powerful dependency analysis application that extracts dependency graphs and mines them for useful information. This application comes in many forms for your ease of use, including command-line tools, a Swing-based application, a web application ready to be deployed in an application server, and a set of Ant tasks.

DoctorJ
Beyond the level of what Javadoc does, DoctorJ compares documentation against code.

FindBugs
This is the web page for FindBugs, a program which looks for bugs in Java code.  It is free software, distributed under the terms of the Lesser GNU Public License.

Hammurapi
Hammurapi is an Open Source Java code review tool. It has more than 120 embedded Inspectors and such unique features as waivers, autowaivers and cascading rulesets.

JCSC
JCSC is a powerful tool to check source code against a highly definable coding standard and potential bad code.
The standard covers naming conventions for class, interfaces, fields, parameter, ... .

JDepend
JDepend traverses Java class file directories and generates design quality metrics for each Java package. JDepend allows you to automatically measure the quality of a design in terms of its extensibility, reusability, and maintainability to effectively manage and control package dependencies.

JLint
Jlint will check your Java code and find bugs, inconsistencies and synchronization problems by doing data flow analysis and building the lock graph.