By default, classes are compiled against the bootstrap and extension classes of the JDK that javac shipped with. But javac also supports cross-compiling , where classes are compiled against a bootstrap and extension classes of a different Java platform implementation. The default is to generate class files to be compatible with both 1.1 and 1.2 VMs. This is the default. 1.2 Generate class files that will run on 1.2 VMs, but will not run on 1.1 VMs.
Directories is a colon-separated list of directories.
Each JAR archive in the specified directories is searched for class files. Recursively search all reachable classes for more recent source files to recompile. This option will more reliably discover classes that need to be recompiled, but can slow down the compilation process drastically. By default, compiler messages go to System.err . Describe how paths and standard extensions were searched to find source and class files.