Cross-Compilation Example

Cross-Compilation Example

The following example uses javac to compile code that will run on a 1.6 VM.

$ javac -source 1.6 -target 1.6
-bootclasspath /usr/local/java/jdk1.6.0_32/jre/lib/rt.jar -extdirs ""
*.java

The -source 1.6 option specifies that version 1.6 (or 6) of the Java programming language be used to compile OldCode.java. The option -target 1.6 option ensures that the generated class files will be compatible with 1.6 VMs. Note that in most cases, the value of the -target option is the value of the -source option; in this example, you can omit the -target option.
You must specify the -bootclasspath option to specify the correct version of the bootstrap classes (the rt.jar library). If not, the compiler generates a warning:

$ javac -source 1.6 *.java

warning: [options]
bootstrap class path not set in conjunction with -source 1.6

If you do not specify the correct version of bootstrap classes, the compiler will use the old language rules (in this example, it will use version 1.6 of the Java programming language) combined with the new bootstrap classes, which can result in class files that do not work on the older platform (in this case, Java SE 6) because reference to non-existent methods can get included.