java - How to index a multimap based on several criteria? -

i have list of "someclass" may consist of lot of functionally equal objects, , need group these. entries identical getname(), getinputdate(), getoutputdate() , getvalue() should grouped together. came across multimap seems need, can't figure out elegant way how group these.

currently have used them key multimap, don't think best solution..

private immutablelistmultimap<string, someclass> getgrouped() {         return multimaps.index                 (someclasslist, new function<someclass, string>() {                     public string apply(someclass someclass) {                         return someclass.getname() + someclass.getinputdate() + someclass                                 .getoutputdate() + someclass.getvalue();                     }                 }); } 

the problem code key. collapsing value string in order obtain key not idea. create key object , use rest of code:

public class persongroup{     private string name;     private date input;     private date output;     private string value;      public persongroup(string name, date input, date output, string value) {         this.name = name;         this.input = input;         this.output = output;         this.value = value;     }      @override     public boolean equals(object o) {         if (this == o) return true;         if (o == null || getclass() != o.getclass()) return false;          persongroup = (persongroup) o;          if (input != null ? !input.equals(that.input) : that.input != null) return false;         if (name != null ? !name.equals(that.name) : that.name != null) return false;         if (output != null ? !output.equals(that.output) : that.output != null) return false;         if (value != null ? !value.equals(that.value) : that.value != null) return false;          return true;     }      @override     public int hashcode() {         int result = name != null ? name.hashcode() : 0;         result = 31 * result + (input != null ? input.hashcode() : 0);         result = 31 * result + (output != null ? output.hashcode() : 0);         result = 31 * result + (value != null ? value.hashcode() : 0);         return result;     } } 

update code like

private immutablelistmultimap<persongroup, someclass> getgrouped() {         return multimaps.index                 (someclasslist, new function<someclass, persongroup>() {                     public persongroup apply(someclass someclass) {                         return new persongroup(someclass.getname(), someclass.getinputdate(), someclass                                 .getoutputdate(), someclass.getvalue());                     }                 });     }