compile error: cannot find symbol: In, StdIn and StdOut
java
Solution
Classes `StdIn`, `StdOut` and `In` aren't part of the standard Java libraries. They're support classes provided to go along with the Princeton course.
From the 1.1 Programming Model page linked in the source code:
Standard input and standard output. `StdIn.java` and `StdOut.java` are 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.java` and `Out.java` are object-oriented versions that support multiple input and output streams, including reading from a file or URL and writing to a file.
So if you want to use the binary search code as-is, you'll need to download those files.
Problem
The code is from http://algs4.cs.princeton.edu/11model/BinarySearch.java.html for Algorithms textbook. ``` 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 ``` $ 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 ```