What is this .dummy.class error from my :JAVA: makefile?

    make: don't know how to make .ALL : .dummy.class

This error may come up if your makefile or project global makefile sets .MAIN either explicitly or from :ALL: because the Java rules also use .MAIN to make the classes. Add the following line to your :JAVA: makefile after your default .MAIN setting. If it is coming from an included makefile then it must come somewhere after the include statement.

    .MAIN : .CLEAR

Details

.dummy.class is defined as the default list of generated class files in the Java rules. The list is overwritten with the real list of generated classes after JavaDeps is run. However when .MAIN defines another default target JavaDeps doesn't get triggered and the list of classes doesn't get redefined so nmake tries to make .dummy.class.