如何将ArrayList<String>中的所有值相加或转换为ArrayList<Integer>

Question

我试图将ArrayList中的所有值加起来，但是没有任何东西允许我得到和。我必须找到从文本文件中提取的数字的平均值。

public static void main(String[] args) throws IOException {
    File file = new File("C:\\Users\\[REDACTED]\\Desktop\\mbox.txt");
    Scanner inputFile = new Scanner(file);
    ArrayList<Integer> ConfidenceLevels = new ArrayList<>();
    String [] DSPAM;
    String line;
    
    while(inputFile.hasNext())
    {
        line = inputFile.nextLine();
        if(line.startsWith("X-DSPAM-Confidence:"))
        {
            DSPAM = line.split(" 0");
            int x = Integer.parseInt(DSPAM[1].trim());
            ConfidenceLevels.add(x);
        }
    }
    System.out.println(ConfidenceLevels);
    System.out.println(ConfidenceLevels.size());
}

Answer 1

您只是在列表中添加元素。如果您需要它们的和，您可以创建一个Integer变量并添加它。

public static void main(String[] args) throws IOException {
    File file = new File("C:\\Users\\[REDACTED]\\Desktop\\mbox.txt");
    Scanner inputFile = new Scanner(file);
    Integer confidenceLevelsSum = 0;
    String [] DSPAM;
    String line;
    
    while(inputFile.hasNext())
    {
        line = inputFile.nextLine();
        if(line.startsWith("X-DSPAM-Confidence:"))
        {
            DSPAM = line.split(" 0");

            // Check if it's null before trying to convert it.
            if (DSPAM[1] == null) {
                continue;
            }

            int x = Integer.parseInt(DSPAM[1].trim());
            confidenceLevelsSum += x;
        }
    }
    System.out.println(confidenceLevelsSum);
}

Answer 2

您可以尝试使用IntSummaryStatistics，您可以得到这个列表的最小/最大值/平均值/和。

    IntSummaryStatistics intSummaryStatistics = ConfidenceLevels.stream().mapToInt(Integer::intValue).summaryStatistics();
    System.out.println(intSummaryStatistics.getAverage());
    System.out.println(intSummaryStatistics.getMin());
    System.out.println(intSummaryStatistics.getMax());
    System.out.println(intSummaryStatistics.getSum());