编译错误:找不到符号:In,StdIn和StdOut

Question

代码来自 http://algs4.cs.princeton.edu/11model/BinarySearch.java.html for Algorithms教科书.

import java.util.Arrays;

public class BinarySearch {

    // precondition: array a[] is sorted
    public static int rank(int key, int[] a) {
        int lo = 0;
        int hi = a.length - 1;
        while (lo <= hi) {
            // Key is in a[lo..hi] or not present.
            int mid = lo + (hi - lo) / 2;
            if      (key < a[mid]) hi = mid - 1;
            else if (key > a[mid]) lo = mid + 1;
            else return mid;
        }
        return -1;
    }

    public static void main(String[] args) {
        int[] whitelist = In.readInts(args[0]);

        Arrays.sort(whitelist);

        // read key; print if not in whitelist
        while (!StdIn.isEmpty()) {
            int key = StdIn.readInt();
            if (rank(key, whitelist) == -1)
                StdOut.println(key);
        }
    }
}

我收到这个错误

$ javac BinarySearch.java 
BinarySearch.java:44: cannot find symbol
symbol  : variable In
location: class BinarySearch
        int[] whitelist = In.readInts(args[0]);
                          ^
BinarySearch.java:49: cannot find symbol
symbol  : variable StdIn
location: class BinarySearch
        while (!StdIn.isEmpty()) {
                ^
BinarySearch.java:50: cannot find symbol
symbol  : variable StdIn
location: class BinarySearch
            int key = StdIn.readInt();
                      ^
BinarySearch.java:52: cannot find symbol
symbol  : variable StdOut
location: class BinarySearch
                StdOut.println(key);
                ^
4 errors

Answer 1

类StdIn,StdOut而In不是标准的Java库的一部分.他们提供的支持课程与普林斯顿大学课程一致.

从源代码中链接的1.1 Programming Model页面:

标准输入和标准输出.StdIn.java并且StdOut.java是用于从标准输入读取数字和文本以及将数字和文本打印到标准输出的库.我们的版本比相应的Java版本具有更简单的界面(并提供了一些技术改进).

...

In.java并且Out.java是面向对象的版本,支持多个输入和输出流,包括从文件或URL读取和写入文件.

因此,如果您希望按原样使用二进制搜索代码,则需要下载这些文件.

Answer 2

如果您已经设置了本课程推荐的环境,则只需将此行添加到您的java文件中

import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;