%{$self->{_hash}} = ();

##</code><code>##

    $self->{_hash} = {};

##</code><code>##

this is cat data
cat:a,b,c,d,e,fcat2:g,h,i,j,k,l,m
this is cat keys
catcat2
this is dog data
dog1:1,2,3,4,5,6,7dog2:21,22,23,24,25
this is dog keys
dog1dog2

but....after creates the second object
this is cat data
cat:a,b,c,d,e,fcat2:g,h,i,j,k,l,m
this should be cat keys
catcat2
this is dog data
dog1:1,2,3,4,5,6,7dog2:21,22,23,24,25
this is dog keys
dog1dog2