arraylist - How To Return number of duplicate string in the array list compare to another array list JAVA -

i need return how many time word duplicate if exist in arraylist.

more explanation: if word in first arraylist exist in arraylist wanna check how many times duplicate in second array list not working?

public int duplication(arraylist<string> studentlist, arraylist<string> teacherlist){     set<string> uniquestudent = new hashset<string>(studentlist);     set<string> uniqueteacher = new hashset<string>(teacherlist);      (string studentkey : uniquestudent) {         (string teacherkey : uniqueteacher) {             if(teacherkey.equals(studentkey)){                 return collections.frequency(studentlist, studentkey);             }         }     }  }     

the right datastructure store duplicates being considered map , below code:

public static void main(string[] args) {     map<string, integer> duplicatesmap = duplicate(             new arraylist<string>(arrays.aslist(new string[] { "a", "h",                     "t", "p", "s", "o", "f", "x", "a" })),             new arraylist<string>(arrays.aslist(new string[] { "a", "h",                     "t", "p", "s", "o", "f", "a", "o", "b", "x", "r" })));     (map.entry<string, integer> entry : duplicatesmap.entryset()) {         system.out.println(entry.getkey() + " found " + entry.getvalue()                 + " times");     } }  public static map<string, integer> duplicate(arraylist<string> fromlist,         arraylist<string> tolist) {     map<string, integer> returnmap = new hashmap<string, integer>();     set<string> uniquefromlist = new hashset<string>(fromlist);     (string key : uniquefromlist) {         if (tolist.contains(key)) {             returnmap.put(key, collections.frequency(tolist, key));         }     }     return returnmap; } 

output

t found 1 times f found 1 times found 2 times p found 1 times s found 1 times o found 2 times h found 1 times x found 1 times