java - Refactoring code to be Generics and functional interface -

i have 2 interfaces 1 can used find statistics key , value , other used visit object , iterate on it, first 1 has following methods:

public interface statistic {      public string getkey();      public object getvalue();      public string getdetails(); } 

and here implementation it:

public class collector implements statistic {      private string key;     private int val;      public collector(string key, int val) {         this.key = key;         this.val = val;     }      public void setvalue(int val) {         this.val = val;     }      @override     public string getkey() {         return key;     }      @override     public integer getvalue() {         return val;     }      @override     public string getdetails() {         return null;     } } 

and other 1 has following:

public interface statisticscollector<t extends object, s extends statistic> {      public string getname();      public void visit(t object);      public iterator<s> calculatedstatistics(); } 

and here implementation it:

public class calculatefromobject<k, v> implements statisticscollector<object, collector> {      employeevalidator empvalidator = new employeevalidator();     stringvalidator strvalidator = new stringvalidator();      @override     public string getname() {         return null;     }      @override     public void visit(object object) {         if (object instanceof string) {             string str = object.tostring();              int uppercasecount = strvalidator.uppercasefreq(str);             strvalidator.set.add(new collector("upper case letters: ", uppercasecount));             int lowercasecount = strvalidator.lowercasefreq(str);             strvalidator.set.add(new collector("lower case letters: ", lowercasecount));             int digitscount = strvalidator.digitfreq(str);             strvalidator.set.add(new collector("digits count: ", digitscount));             int wordcount = strvalidator.wordfreq(str);             strvalidator.set.add(new collector("words count: ", wordcount));             int nonwordcount = strvalidator.nonwordfreq(str);             strvalidator.set.add(new collector("non word count: ", nonwordcount));          } else if (object instanceof employee) {              employee emp = (employee) object;             empvalidator.salaryvalidator(emp);             empvalidator.birthdatevalidator(emp);             empvalidator.birthplacevalidator(emp);             empvalidator.resignationdatevalidator(emp);             empvalidator.positionvalidator(emp);         }     }      @override     public iterator<collector> calculatedstatistics() {         return empvalidator.set.iterator();     }   } 

and in package have bean employee has few properties firstname, lastname, salary , position setters , getters.

i validations me number of employees has salary of x , been born in 1990 , did following class these validations:

public class employeevalidator {      public set<collector> set = new hashset<>();      public void salaryvalidator(employee emp) {         int count = 0;         // each collector consist of condition (function), key, value (always incremented)         if (emp.getsalary() < 350) {             set.add(new collector("employee salaries less 350jd: ", ++count));         } else if (emp.getsalary() >= 350 && emp.getsalary() < 600) {             set.add(new collector("employee salaries between 350jd , 600jd: ", ++count));         } else if (emp.getsalary() >= 600 && emp.getsalary() < 1200) {             set.add(new collector("employee salaries between 600jd , 1200jd ", ++count));         } else if (emp.getsalary() >= 1200) {             set.add(new collector("employee salaries more 1200jd: ", ++count));         }      }      public void birthdatevalidator(employee emp) {         (collector stats : set) {             if (("employees born in " + emp.getbirthdate().getyear() + " = ").equals(stats.getkey())) {                 count(stats);                 return;             }         }         set.add(new collector("employees born in " + emp.getbirthdate().getyear() + " = ", 1));     }      public void birthplacevalidator(employee emp) {         (collector stats : set) {             if (("employees born in " + emp.getbirthplace() + " = ").equals(stats.getkey())) {                 count(stats);                 return;             }         }         set.add(new collector("employees born in " + emp.getbirthplace() + " = ", 1));     }      public void resignationdatevalidator(employee emp) {         (collector stats : set) {             if (("employees resignation in " + emp.getresignationdate().getyear() + " = ").equals(                     stats.getkey())) {                 count(stats);                 return;             }         }         set.add(new collector("employees resignation in " + emp.getresignationdate().getyear() + " = ", 1));     }      public void positionvalidator(employee emp) {         (collector stats : set) {             if (("employees occupy " + emp.getposition() + " position = ").equals(stats.getkey())) {                 count(stats);                 return;             }         }         set.add(new collector("employees occupy " + emp.getposition() + " position = ", 1));     }      private void count(collector stats) {         int counter = stats.getvalue() + 1;         stats.setvalue(counter);     } } 

and have class validate strings , see how many uppercase letters string has, how many lower case has...etc

as can see in visit method in calculatefromobject class im calling methods validations, working fine , getting expected results, code not efficient make generic , make accept type of object, have done few tries im stuck.

i have tried write functional interface called conditions has 1 method can pass condition , check following:

public interface conditions {      boolean checkcondition(object obj);  } 

so can suggest best way change code generic , accept type of objects student example , clean possible maybe applying design pattern?

there's lot of overhead in classes , misunderstanding of interfaces against pojo's (simple classes). on high level should following:

1). remove interface statistic , class collectors. incapsulating data. instead - create pojo employee necessary fields + getters + setters. don't use 'key-value`, give fields meaningful names:

public class employee {     private string name;     private int id;     private double salary;         ...      public string getname() {...}      public void setname(..) {...} // other getters / setters } 

create constructor if needed

2) looks employee class redundant, remove it. use new employee instead 3) use collections framework store collections of employee's instances.

`list<employee> employees = new arraylist<>(); employees.add(new employee(.... )); ` 

4). create interface employeevalidator validating methods , implement it:

public interface employeevalidator { void validate(list<employee> employees); }

5) if want operate statistics data, create separate statistics class operate on collections of employees, e.g.

public class statistics {      public double getavgsalary(list<employee> employees)     {         double avgsalary = 0;         (employee e : employees) {         ....         }     } }