/*<?php
  //*/public class PhpJava { public static void main(String[] args) { System.out.printf("/*%s",
  //\u000A\u002F\u002A
  class PhpJava {
      static function main() {
          echo(//\u000A\u002A\u002F
          "Hello World!");
  }}
  //\u000A\u002F\u002A
  PhpJava::main();
  //\u000A\u002A\u002F

It's both valid PHP and Java.

Not mine, stolen from https://gist.github.com/forairan/b1143f42883b3b0ee1237bc9bd0....