为什么java.util.Scanner存在？

Question

可能重复： 扫描仪与BufferedReader

是否存在使用java.util.Scanner来读取某种输入的情况？在我的小测试中，我发现与java.util.Bufferedreader或从java.util.InputStreamReader实现自己的阅读器相比，它非常慢。

那我为什么要用扫描仪呢？

Answer 1

Scanner类的主要用途是使用正则表达式解析原始类型和字符串的文本。您可以提供几种要读取的资源类型。

Answer 2

来自文档

一个简单的文本扫描器，它可以使用正则表达式解析基本类型和字符串。

不会做BufferedReader的。

Answer 3

虽然扫描仪速度相对较慢，但它往往足够快，而且比BufferedReader强大得多。

public static void main(String... args) throws IOException {

    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < 10000; i++)
        sb.append("line: ").append(i).append("\n");
    String lines = sb.toString();

    for (int i = 0; i < 6; i++) {
        testBufferedReader(lines);
        testScanner(lines);
    }
}

private static void testBufferedReader(String text) throws IOException {
    int count = 0;
    BufferedReader br = new BufferedReader(new StringReader(text));
    long start = System.nanoTime();
    while (br.readLine() != null)
        count++;
    long time = System.nanoTime() - start;
    System.out.printf("BufferedReader.readLine() took an average of %,d ns count=%,d%n", time / count, count);
}

private static void testScanner(String text) throws IOException {
    int count = 0;
    Scanner sc = new Scanner(new StringReader(text));
    long start = System.nanoTime();

    while (sc.hasNextLine()) {
        sc.nextLine();
        count++;
    }

    long time = System.nanoTime() - start;
    System.out.printf("Scanner nextLine took an average of %,d ns count=%,d%n", time / count, count);
}

最后打印

BufferedReader.readLine() took an average of 124 ns count=10,000
Scanner nextLine took an average of 1,549 ns count=10,000

虽然相对差异很大，但扫描仪每台不到几微秒.