My apologies in advance for any miss-speakings here as I am new to MinGW (and gcc):
I recently installed MinGW using the MinGW-5.1.3 installer and chose the Java (gcj) component to install.  For version reference, the installation included the file MinGW\share\java\libgcj-3.4.5.jar.
I have since been able to create and successfully test a HelloWorld.exe generated from a file.  So far so good.
I am now trying to use gcj to similarly create an executable for my "real" java application, however, I am getting an error at compile time indicating this line from one of the Java files:
    File xmlFile = new File(new URI(extForm));
The message is:
    com/cfg/ In class `com.cfg.MDLoader':
    com/cfg/MDLoader'.java: In method `com.cfg.MDLoader'.nstdLoad(com.core.ext.TL,java.lang.String,com.cfg.MD)':
    com/cfg/MDLoader'.java:117: error: class '' has no method named '<init>' matching signature '(Ljava/net/URI;)V'
    com/cfg/MDLoader'.java:117: error: expected type 'null' but stack contains 'void'
    com/cfg/MDLoader'.java:118: confused by earlier errors, bailing out
According to Sun's documentation, the class has had the API to create a new File object taking only a URI since jdk 1.4, and according to a link off od GNU's site, their support for jdk 1.4 support is 99.84% complete (I actually couldn't find what comprised the .06%).
Finally, my question is; what level of JDK support am I getting through my MinGW libgcj-3.4.5.jar - level installation, and is there anyway to update/modify my installation to take advantage of the more-recent level of jdk support available from the GNU's latest gcj/classpath releases?