my $query = new MyPackage::Query("utf8"); 
my $query2 = new MyPackage::Query("euc-jp");

##</code><code>##

sub new {
    my $class = shift;
    $self->{input_enc} = shift;  
    
    unless (defined $self->{input_enc}) {
	$self->{input_enc} = "euc-jp";
    }

    #...

    bless($self, $class);
    return $self;
}