java - Sorting objects by fields subsequently -

the issue sort huge collection of pojo objects

class entity{     string key1;     string key2;     string key3;     string key4; } 

in alphabetical order of fields subsequently. means first sorting key1, key2 , etc. of key can null. question simplest way that.

a way append keys together , use comparator<entity> -

// keys of entity appended , compared other entity int compare(entity e1, entity e2){   return appendandhandlenull(e1.key1, e1.key2, e1.key3).compareto(appendandhandlenull(e2.key1, e2.key2, e2.key3)); }    /**   * method keys of entity in appended form  */ private static final string appendandhandlenull(string list...){    stringbuilder result = new stringbuilder ();    for(string s : list){       result.append(s!=null?s:"").append(" ");//note: space appended after each key    }    return result.tostring(); } 

what doing here is..... keys of entity appended in order in comparison need done, , compared other entity.

you might need trim each value before appending.

edited: necessary seperate each key space code work properly.

code fixed above. @thilo pointing it.