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. This is the default. 1.2 Generate class files that will run on VMs in the Java 2 SDK, v 1.2 and later, but will not run on 1.1 VMs. 1.3 Generate class files that will run on VMs in the Java 2 SDK, v 1.3 and later, but will not run on 1.1 or 1.2 VMs.
Directories is a semicolon-separated list of directories.
Each JAR archive in the specified directories is searched for class files. These options are supported only by oldjavac . They are not supported by the new javac compiler. Display information about non-standard options and exit. Recursively search all reachable classes for more recent source files to recompile.