Sum value Of Class Objects Property In ArrayList

Question

I have an ArrayList which having many objects. I want to do sum of values of the same property name.

Examples Data in Array List which is Objects of

Answer 1

I'd iterate the list and collect the results in a map:

public static List sumPerLedgerName
    (List list) {

    Map map = new HashMap<>();

    for (ProfitAndLossDataDO p : list) {
        String name = p.getLedgerName();
        ProfitAndLossDataDO sum = map.get(name);
        if (sum == null) {
            sum = new ProfitAndLossDataDO(name, 0.0);
            map.put(name, sum);
        }
        sum.setLedgerAmount(sum.getLedgerAmount() + p.getLedgerAmount());
    }
    return new ArrayList<>(map.values());
}

EDIT:

Java 8's enhancements to the Map interface allow us to implement this method in a slightly more elegant way, with the annoying if block in the middle:

public static List sumPerLedgerName
    (List list) {

    Map map = new HashMap<>();

    for (ProfitAndLossDataDO p : list) {
        String name = p.getLedgerName();
        ProfitAndLossDataDO sum = map.computeIfAbsent(name, n -> new ProfitAndLossDataDO(n, 0.0));
        sum.setLedgerAmount(sum.getLedgerAmount() + p.getLedgerAmount());
    }
    return new ArrayList<>(map.values());
}