将列表总结为流的限制

Question

如何获取记录，计数总和应该在限制内。在下面的示例中，Records对象包含 recordId 和计数，我想根据计数的总和应该小于或等于我的限制条件来获取记录数据。

public class Records {
    private int recordID;
    private int count;

    public Records(int recordID, int count) {
        this.recordID = recordID;
        this.count = count;
    }

    public int getRecordID() {
        return recordID;
    }

    public void setRecordID(int recordID) {
        this.recordID = recordID;
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }
}


public static void main(String[] args) {
    
    final List<Records> recordList = new ArrayList<>();
    
    recordList.add(new Records(100, 10));
    recordList.add(new Records(501, 20));
    recordList.add(new Records(302, 5));
    recordList.add(new Records(405, 2));
    recordList.add(new Records(918, 8));
    int limit = 35;
}

预期结果

recordList 应该有记录对象：[100,10], [500,20], [302,5] 记录

Answer 1

使用 Stream API 解决此问题的问题是，您必须将一些信息保留在处理上下文之外，并同时读取/更新（依赖）它。这些任务不适合 Stream API。

使用 for 循环来代替，它非常适合并且非常适合于此：

int index = 0;                              // highest index possible
int sum = 0;                                // sum as a temporary variable
for (int i=0; i<recordList.size(); i++) {   // for each Record
    sum += recordList.get(i).getCount();    // ... add the 'count' to the 'sum'
    if (sum <= limit) {                     // ... until the sum is below the limit
        index = i;                          // ... move the pivot
    } else break;                           // ... or else stop processing
}

// here you need to get the list from 0 to index+1 
// as long as the 2nd parameter of subList(int, int) is exlcusive
List<Record> filteredRecords = recordList.subList(0, index + 1);