- source: The version that your source code requires to compile.
- target: The oldest JRE version you want to support.
Be sure to also set bootclasspath to ensure your program will work on older VMs.
The following example uses javac to compile code that will run on a 1.6 VM.
C\:>javac -source 1.6 -target 1.6 -bootclasspath C:\jdk1.6.0\lib\rt.jar -extdirs "" OldCode.java
-source 1.6option specifies that version 1.6 (or 6) of the Java programming language be used to compile
OldCode.java. The option
-target 1.6option ensures that the generated class files will be compatible with 1.6 VMs. Note that in most cases, the value of the
-targetoption is the value of the
-sourceoption; in this example, you can omit the
You must specify the
-bootclasspathoption to specify the correct version of the bootstrap classes (the
rt.jarlibrary). If not, the compiler generates the following warning:
C:\>javac -source 1.6 OldCode.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.