java - 减少对象列表中的整数属性

Question

我有这个结构的模型

public class MyModel {
        private long firstCount;
        private long secondCount;
        private long thirdCount;
        private long fourthCount;

        public MyModel(firstCount,secondCount,thirdCount,fourthCount) 
        {
        }
        //Getters and setters

}  

假设我有一个包含以下数据的模型列表

MyModel myModel1 = new MyModel(10,20,30,40);
MyModel myModel2 = new MyModel(50,60,70,80);

List<MyModel> modelList = Arrays.asList(myModel1, myModel2);

假设我想找出所有模型中 firstCount 的总和，我可以这样做

Long collect = modelList.stream().collect
(Collectors.summingLong(MyModel::getFirstCount));

如果我想一次性找出所有模型中的属性总和怎么办？有什么方法可以实现吗？

输出应该是这样的

• firstCount 的总和 = 60
• secondCount 的总和 = 80
• thirdCount 的总和 = 100
• fourthCount 的总和 = 120

Answer 1

使用 MyModel 作为累加器:

MyModel reduced = modelList.stream().reduce(new MyModel(0, 0, 0, 0), (a, b) ->
                      new MyModel(a.getFirstCount() + b.getFirstCount(),
                                  a.getSecondCount() + b.getSecondCount(),
                                  a.getThirdCount() + b.getThirdCount(),
                                  a.getFourthCount() + b.getFourthCount()));
System.out.println(reduced.getFirstCount());
System.out.println(reduced.getSecondCount());
System.out.println(reduced.getThirdCount());
System.out.println(reduced.getFourthCount());