ArrayList中类对象属性的总和

ArrayList中类对象属性的总和

我会遍历列表并将结果收集在地图中：

public static List<ProfitAndLossDataDO> sumPerLedgerName    (List<ProfitAndLossDataDO> list) {    Map<String, ProfitAndLossDataDO> 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());}

编辑：

Java
8对

Map

接口的增强使我们能够以一种稍微更优雅的方式来实现此方法，

if

中间是令人讨厌的代码块：

public static List<ProfitAndLossDataDO> sumPerLedgerName    (List<ProfitAndLossDataDO> list) {    Map<String, ProfitAndLossDataDO> 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());}