如何在java中的arraylist中的每个第3个元素之后添加换行符？ [英] How to Add newline after every 3rd element in arraylist in java?

问题描述

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：

My program need to add newline after every 3rd element in the arraylist. Here is my input file which contain the following data:

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，

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,

它会继续多行。

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;
        } 
    }
}

推荐答案

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。如果真的多，你可以在构建它时迭代它。

I changed your code to read using the "new" Java 7 files I/O and corrected the use of a line separator, along with some formatting. Here I iterate over the list after it was completed. If it is really long you can iterate over it while constructing it.

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;
    }
}

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