Question

我的程序需要在arraylist中的每个第3个元素之后添加换行符。这是我的输入文件，其中包含以下数据：

934534519137441534534534366,0796544345345345348965， 796345345345544894534565,734534534596544534538965， 4058991374534534999999,34534539624,91953413789453450452， 9137534534482080,9153453459137482080,405899137999999， 9653453564564524,91922734534779797,0834534534980001528,82342398534 6356343430001528,405899137999999,9191334534643534547423752， 3065345782642564522021,826422205645345345645621， 40584564563499137999999,953453345344624,3063454564345347， 919242353463428434451,09934634634604641264,990434634634641264， 40346346345899137999999,963445636534653452,919234634643325857953， 91913453453437987385,59049803463463453455421,405899137534534999999， 9192273453453453453758434，

它继续多行。

代码：

public class MyFile {

    private static final Pattern ISDN =Pattern.compile("\\s*ISDN=(.*)");

    public List<String> getISDNsFromFile(final String fileName) throws IOException {

        final Path path = Paths.get(fileName);
        final List<String> ret = new ArrayList<>();
        Matcher m;
        String line;
        int index = 0;
        try (
        final BufferedReader reader = Files.newBufferedReader(path, StandardCharsets.UTF_8);) {
            while ((line = reader.readLine()) != null) {
                m = ISDN.matcher(line);
                if (m.matches()) {
                    ret.add(m.group(1));
                    index++;
                    if(index%3==0){
                        if(ret.size() == index){
                            ret.add(m.group(1).concat("\n"));
                        }
                    }
                }
            }
            return ret;
        } 
    }
}

Answer 1

我使用“新”Java 7文件I / O将代码更改为读取并更正了行分隔符的使用以及一些格式。在这里，我在完成后迭代列表。如果它真的很长，你可以在构建它时迭代它。

public class MyFile {

    private static final Pattern ISDN = Pattern.compile("\\s*ISDN=(.*)");
    private static final String LS = System.getProperty("line.separator");

    public List<String> getISDNsFromFile(final String fileName) throws IOException {

        List<String> ret = new ArrayList<>();
        Matcher m;

        List<String> lines = Files.readAllLines(Paths.get(fileName), StandardCharsets.UTF_8);
        for (String line : lines) {
            m = ISDN.matcher(line);
            if (m.matches())
                ret.add(m.group(1));
        }
        for (int i = 3; i < ret.size(); i+=4)
            ret.add(i, LS);
        return ret;
    }
}

Answer 2

我认为您不需要将arraylist的大小与索引进行比较。只需删除该条件并尝试使用此

if(index%3==0){                         
   ret.add(System.getProperty("line.separator"));
   }

虽然我支持@Peter的评论 I would add them all to a List and only add the formatting when you print. Adding formatting in your data usually leads to confusion.

如何在java中的arraylist中的每个第3个元素之后添加换行符？

代码：

2 个答案: