Find current JVM, either from java builtin property or from $JAVA_HOME

JavaHome.jar

JavaHome.java

/*

Find current JVM, either from java builtin property or from $JAVA_HOME

$ javac JavaHome.java
$ java JavaHome
/usr/lib/jvm/java-8-openjdk-amd64/jre
(Info: /usr/lib/jvm/java-8-openjdk-amd64/jre from builtin)
$ java -jar /tmp/JavaHome.jar 2>/dev/null
/usr/lib/jvm/java-8-openjdk-amd64/jre
$ jar cfe JavaHome.jar JavaHome JavaHome.class
$ java -jar JavaHome.jar # etc.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.

*/
public class JavaHome {
    public static void main(String[] args) {
        String jh_source;
        String jh_path;
        String jh_property = System.getProperty("java.home");;
        if(System.getenv("JAVA_HOME") == null ){
            jh_path = jh_property;
            jh_source = "builtin";
        }else{
            jh_path = System.getenv("JAVA_HOME");
            jh_source = "environment";
        }
        System.out.printf("%s\n", jh_path);
        System.err.printf("(Info: %s from %s)\n", jh_path, jh_source);
        if (!jh_property.equals(jh_path)) {
            System.err.printf("(Notice: Differs from builtin %s)\n", jh_property);
        }
    }
}

Makefile

all:
        -rm JavaHome.class JavaHome.jar
        javac JavaHome.java
        jar cfe JavaHome.jar JavaHome JavaHome.class