Array In Space Invaders Program

Java Code:

public synchronized boolean isHit (FilledRect missile) {
for (int col = 0; col < aliens[0].length; col++) {
for (int row = 0; row < aliens.length; row++) {
if (aliens[row][col]!= null && aliens[row][col].overlaps (missile)) {
aliens[row][col] = null;
return true;
}
return false;
}
}
} mh_sh_highlight_all('java');

And I get an error saying that it cannot find symbol method overlaps. So is there something wrong that I am doing?