2.1 Standard features not yet supported

This list of compatibility issues is by no means complete.

• gcj implements the JDK 1.2 language. It supports inner classes and the new 1.4 assert keyword. It does not yet support the Java 2 strictfp keyword (it recognizes the keyword but ignores it).
• libgcj is largely compatible with the JDK 1.2 libraries. However, libgcj is missing many packages, most notably java.awt. There are also individual missing classes and methods. We currently do not have a list showing differences between libgcj and the Java 2 platform.
• Sometimes the libgcj implementation of a method or class differs from the JDK implementation. This is not always a bug. Still, if it affects you, it probably makes sense to report it so that we can discuss the appropriate response.
• gcj does not currently allow for piecemeal replacement of components within libgcj. Unfortunately, programmers often want to use newer versions of certain packages, such as those provided by the Apache Software Foundation's Jakarta project. This has forced us to place the org.w3c.dom and org.xml.sax packages into their own libraries, separate from libgcj. If you intend to use these classes, you must link them explicitly with -l-org-w3c-dom and -l-org-xml-sax. Future versions of gcj may not have this restriction.