Установить уровень соответствия компилятора Java

Используйте опции -source и -target:

javac -target 1.6 -source 1.6 Hello.java

Используйте 1_

Эта информация получена при запуске javac -help:

Usage: javac <options> <source files>
where possible options include:
  -g                         Generate all debugging info
  -g:none                    Generate no debugging info
  -g:{lines,vars,source}     Generate only some debugging info
  -nowarn                    Generate no warnings
  -verbose                   Output messages about what the compiler is doing
  -deprecation               Output source locations where deprecated APIs are used
  -classpath <path>          Specify where to find user class files and annotation processors
  -cp <path>                 Specify where to find user class files and annotation processors
  -sourcepath <path>         Specify where to find input source files
  -bootclasspath <path>      Override location of bootstrap class files
  -extdirs <dirs>            Override location of installed extensions
  -endorseddirs <dirs>       Override location of endorsed standards path
  -proc:{none,only}          Control whether annotation processing and/or compilation is done.
  -processor <class1>[,<class2>,<class3>...]Names of the annotation processors to run; bypasses default discovery process
  -processorpath <path>      Specify where to find annotation processors
  -d <directory>             Specify where to place generated class files
  -s <directory>             Specify where to place generated source files
  -implicit:{none,class}     Specify whether or not to generate class files for implicitly referenced files
  -encoding <encoding>       Specify character encoding used by source files
  -source <release>          Provide source compatibility with specified release
  -target <release>          Generate class files for specific VM version
  -version                   Version information
  -help                      Print a synopsis of standard options
  -Akey[=value]              Options to pass to annotation processors
  -X                         Print a synopsis of nonstandard options
  -J<flag>                   Pass <flag> directly to the runtime system

В документе по Java говорится (ищите перекрестную компиляцию опции)

By default, classes are compiled against the bootstrap and extension classes of the platform 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. It is important to use -bootclasspath and -extdirs when cross-compiling; see Cross-Compilation Example below.

-target version

Создайте файлы классов, предназначенные для указанной версии виртуальной машины. Файлы классов будут работать в указанной цели и в более поздних версиях, но не в более ранних версиях виртуальной машины. Допустимые цели: 1,1, 1,2, 1,3, 1,4, 1,5 (также 5), 1,6 (также 6) и 1,7 (также 7). Значение по умолчанию для -target зависит от значения -source:

If -source is not specified, the value of -target is 1.7
If -source is 1.2, the value of -target is 1.4
If -source is 1.3, the value of -target is 1.4
If -source is 1.5, the value of -target is 1.7
If -source is 1.6, the value of -target is 1.7
For all other values of -source, the value of -target is the value of -source.

So,

javac -target 1.6 -source 1.6 yourJavaProgram.java

Используйте команду ниже:

javac -target 1.6 -source 1.6 Hello.java