java - 如何将计数器插入 Stream<String> .forEach()？

Question

FileWriter writer = new FileWriter(output_file);
    int i = 0;

    try (Stream<String> lines = Files.lines(Paths.get(input_file))) {
        lines.forEach(line -> {
            try {
                writer.write(i + " # " + line + System.lineSeparator());
            } catch (Exception e) {
                e.printStackTrace();
            }   
        }
                    );
        writer.close();
    }

我需要用行号写行，所以我尝试在 .forEach() 中添加一个计数器，但我无法让它工作。我只是不知道把 i++ 放在哪里；进入代码，到目前为止，随意乱搞并没有帮助。

Answer 1

您可以使用 AtomicInteger 作为可变 final 计数器。

public void test() throws IOException {
    // Make sure the writer closes.
    try (FileWriter writer = new FileWriter("OutFile.txt") ) {
        // Use AtomicInteger as a mutable line count.
        final AtomicInteger count = new AtomicInteger();
        // Make sure the stream closes.
        try (Stream<String> lines = Files.lines(Paths.get("InFile.txt"))) {
            lines.forEach(line -> {
                        try {
                            // Annotate with line number.
                            writer.write(count.incrementAndGet() + " # " + line + System.lineSeparator());
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
            );
        }
    }
}