java - Data loss from class during for each iteration -

i've got debug outputs in constructor output expected

incoming parameter{c=0.620405, h=0.104122, o=0.275473} stored

parameter{c=0.620405, h=0.104122, o=0.275473}

but when call tostring() while iterating through list returns empty set.

what's causing behavior?

public class pnnlentry {             private string matnum = "";             private string material = "";             private string formula = "";             private string density = "";             private string comment = "";             private string references = "";             //map element weight fraction string             private map<string, string> elements = new treemap<string, string>();          public pnnlentry(){          }         public pnnlentry(string num, string mat, string form, string dens,                  string com, string ref, map<string, string> elem){             matnum = num;            material = mat;            formula = form;            density = dens;            comment = com;            references = ref;            elements = elem;            system.out.println("incoming parameter" + elem.tostring());            system.out.println("stored parameter" + elements.tostring());            system.out.println(this.tostring());         }  @override public string tostring(){     string buff = "\n";      buff += matnum;     buff += ") " + material;     buff += "\t" + formula;     buff += "\n" + density;     buff += "\n" + comment;     buff += "\n" + elements.tostring();      buff += "\n" + references;      return buff; } } 

from structures:

private static pnnlentry entry = new pnnlentry(); private static list<pnnlentry> outlist = new arraylist<pnnlentry>(); 

sample output code

 system.out.println("elements \t " + elements.tostring());  entry = new pnnlentry(matnum, material, formula, density,                          comment, references, elements);  system.out.println(entry.tostring());  outlist.add(entry);  //clear map next element  elements.clear();   ...   for(pnnlentry output : outlist){      system.out.println(output);      system.out.println(output.getelements().tostring());  } 

outputs:

elements {c=0.775501, ca=0.018378, f=0.017422, h=0.101327, n=0.035057, o=0.052316} incoming parameter{c=0.775501, ca=0.018378, f=0.017422, h=0.101327, n=0.035057, o=0.052316} stored parameter{c=0.775501, ca=0.018378, f=0.017422, h=0.101327, n=0.035057, o=0.052316}

1) a-150 tissue-equivalent plastic (a150tep) - 1.127000 above density estimated accurate 4 significant digits. uncertainties not addressed. following data calculated input weight fractions {c=0.775501, ca=0.018378, f=0.017422, h=0.101327, n=0.035057, o=0.052316} density , weight fractions http://physics.nist.gov/cgi-bin/star/compos.pl?matno=099 (nist 1998).

...

1) a-150 tissue-equivalent plastic (a150tep) -
1.127000 above density estimated accurate 4 significant digits. uncertainties not addressed. following data calculated input weight fractions {} density , weight fractions http://physics.nist.gov/cgi-bin/star/compos.pl?matno=099 (nist 1998).

so data being lost map data passed.

my best guess aliasing problem clearing map after it's passed class constructor, i'm not if that's or how best resolve it.

here's problem:

elements.clear(); 

recall inside of constructor, you're doing this:

elements = elem; 

...where elements represents field , elem represents you've passed in. means they're pointing same reference.

you're trying reset state of map, admirable, that's not necessary. 1 of 2 things:

• new instance of map when you're trying insert things...

• ...or use hashmap's copy constructor:

  elements = new hashmap<>(elem);