Question

I have a List of object as List<Human> humanList;
which human object consist of 5 variable as firstname, lastname,color,length,sex.

How can i check out to see the variable(firstname) how many times appear/exist in the list?

    List<Human> humanList = getHumanList();
    for(Human human :humanList){

    }

Answer 1

Assuming here firstname is of type String, if it is not – change it as needed.

Create a Map<String,Integer> (let it be map) which will be used as a histogram.

Iterate the list, and for each human:

Integer temp = map.get(human.firstName); //search for the current number of occurances
if (temp == null) map.put(human.firstName, 1); //first occurance of this firstname
else map.put(human.firstName,temp+1); //not first occurance, modify the map.

When you are done map holds each firstName as a key and the number of its occurances as the matching value.