#!/bin/bash
s=" Some text
// Remove me
Not me
and // not me LOG.debug
// me, too"
sed '/^[[:blank:]]*\/\//d; s/LOG\.debug/System.out.println/g' <<< "$s"
IyEvYmluL2Jhc2gKcz0iICAgU29tZSB0ZXh0CiAvLyBSZW1vdmUgbWUKTm90IG1lCmFuZCAvLyBub3QgbWUgTE9HLmRlYnVnCi8vIG1lLCB0b28iCnNlZCAnL15bWzpibGFuazpdXSpcL1wvL2Q7IHMvTE9HXC5kZWJ1Zy9TeXN0ZW0ub3V0LnByaW50bG4vZycgPDw8ICIkcyIK