Java 编译错误：找不到符号：In、StdIn 和 StdOut
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compile error: cannot find symbol: In, StdIn and StdOut
提问by Jason Kim
The code is from http://algs4.cs.princeton.edu/11model/BinarySearch.java.htmlfor Algorithms textbook.
代码来自 http://algs4.cs.princeton.edu/11model/BinarySearch.java.html算法教科书。
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);
}
}
}
I get this error
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
采纳答案by Jon Skeet
Classes StdIn, StdOutand Inaren't part of the standard Java libraries. They're support classes provided to go along with the Princeton course.
Classes StdIn，StdOut并且In不是标准 Java 库的一部分。它们是与普林斯顿课程一起提供的支持课程。
From the 1.1 Programming Modelpage linked in the source code:
从源代码中链接的1.1 编程模型页面：
Standard input and standard output.
StdIn.javaandStdOut.javaare libraries for reading in numbers and text from standard input and printing out numbers and text to standard output. Our versions have a simpler interface than the corresponding Java ones (and provide a few tecnical improvements)....
In.javaandOut.javaare object-oriented versions that support multiple input and output streams, including reading from a file or URL and writing to a file.
标准输入和标准输出。
StdIn.java和StdOut.java是用于从标准输入读取数字和文本并将数字和文本打印到标准输出的库。我们的版本具有比相应 Java 版本更简单的界面（并提供一些技术改进）。...
So if you want to use the binary search code as-is, you'll need to download those files.
因此，如果您想按原样使用二进制搜索代码，则需要下载这些文件。
回答by Dheeraj Joshi
You can replace then with
你可以用然后替换
Output:
输出：
System.out.println(key);
Input
输入
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String Key= null;
try {
Key = reader.readLine();
} catch (IOException e) {
e.printStackTrace();
}
They are using custom libraries to print the value to console(Presumably) You can redirect the output to console.
他们正在使用自定义库将值打印到控制台（大概）您可以将输出重定向到控制台。
回答by Amir Kost
You should use System.inand System.outinstead of StdInand StdOut.
Create an ObjectInputStreamwrapping the System input stream the following way:ObjectInputStream ois = new ObjectInputStream(System.in);
It has a readIntmethod, amd to check if it is empty, you must catch the EOFException.
您应该使用System.inandSystem.out而不是StdInand StdOut。通过以下方式
创建一个ObjectInputStream包装系统输入流：ObjectInputStream ois = new ObjectInputStream(System.in);
它有一个readInt方法 amd 来检查它是否为空，您必须捕获EOFException.
回答by Gladstone24
StdIn and In are custom Libraries that are included within the algs4 class download. Execute the program with the command java-algs4 instead of just java and it should work.
StdIn 和 In 是包含在 algs4 类下载中的自定义库。使用命令 java-algs4 而不仅仅是 java 执行程序，它应该可以工作。
回答by lohenzoo
If you have already set up the environment recommended for the course, only add this lines to your java file
如果您已经设置了课程推荐的环境，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;
