JBrownie is a wrapper around the system default javac Java compiler, that monitors Java sourcecode and automatically recompiles any files found changed.

The focus of this tool is to assist software developers, who prefer to use a plain text editors over a resourcehungry IDE, but still want their code to be autocompiled on the fly without delay and without having to manually start javac over and over again. Checking for syntax errors becomes now as easy as just saving the file in question.

Platform:Cross platform;                             License:unknown

Reference:https://www.onyxbits.de/jbrownie

Jikes is a compiler that translates Java source files as defined in The Java Language Specification into the bytecoded instruction set and binary format defined in The Java Virtual Machine Specification.

You may wonder why the world needs another Java compiler, considering that Sun provides javac free with its SDK. Jikes has five advantages that make it a valuable contribution to the Java community:

Features:

Open source. Jikes is OSI Certified Open Source Software.OSI Certified is a certification mark of the Open Source Initiative.

Strictly Java compatible. Jikes strives to adhere to both The Java Language Specification and The Java Virtual Machine Specification as tightly as possible, and does not support subsets, supersets, or other variations of the language. The FAQ describes some of the side effects of this strict language conformance.

High performance. Jikes is a high performance compiler, making it ideal for use with larger projects.

Dependency analysis. Jikes performs a dependency analysis on your code that provides two very useful features: Incremental builds and makefile generation.

Constructive Assistance. Jikes strives to help the programmer write better code in two key ways. Jikes has always strived to provide clear error and warning text to assist the programmer in understanding problems, and now with release 1.19 Jikes helps point out common programming mistakes as documented in Effective Java.

Platform:Linux ;                                  License:IBM Public License

Reference:https://jikes.sourceforge.net/

GCJ is a portable, optimizing, ahead-of-time compiler for the Java Programming Language. It can compile Java source code to Java bytecode (class files) or directly to native machine code, and Java bytecode to native machine code.

Compiled applications are linked with the GCJ runtime, libgcj, which provides the core class libraries, a garbage collector, and a bytecode interpreter.libgcj can dynamically load and interpret class files, resulting in mixed compiled/interpreted applications. It has been merged with GNU Classpath and supports most of the 1.4 libraries plus some 1.5 additions.

Platform:Cross platform;                   License: GNU Public License

Reference:https://gcc.gnu.org/java/