从文本文件中读取某些行

Question

我想从文本文件中读取第1,第4,第7等(每3行),但我不知道如何继续这样做,因为nextLine()按顺序读取所有内容.谢谢你的建议？

Scanner in2 = new Scanner(new File("url.txt"));

while (in2.hasNextLine()) {
    // Need some condition here
    String filesURL = in2.nextLine();
}

Answer 1

使用计数器和%(模数)运算符,因此只读取每三行.

Scanner in = new Scanner(new File("url.txt"));

int i = 1;

while (in.hasNextLine()) {
    // Read the line first
    String filesURL = in.nextLine();

    /*
     * 1 divided by 3 gives a remainder of 1
     * 2 divided by 3 gives a remainder of 2
     * 3 divided by 3 gives a remainder of 0
     * 4 divided by 3 gives a remainder of 1
     * and so on...
     * 
     * i++ here just ensures i goes up by 1 every time this chunk of code runs.
     */
    if (i++ % 3 == 1) {
        // On every third line, do stuff; here I just print it
        System.out.println(filesURL);
    }
}

Answer 2

您阅读每一行但只处理每三行一次:

int lineNo = 0;
while (in2.hasNextLine()) {
    String filesURL = in2.nextLine();
    if (lineNo == 0)
        processLine (filesURL);
    lineNo = (lineNo + 1) % 3;
}

在lineNo = (lineNo + 1) % 3将循环lineNo通过0,1,2,0,1,2,0,1,2,...时,它的线与将仅被处理零(因此线1,4,7,...).