compile error: cannot find symbol: In, StdIn and StdOut
<p>The code is from 
<a href="http://algs4.cs.princeton.edu/11model/BinarySearch.java.html" rel="nofollow">http://algs4.cs.princeton.edu/11model/BinarySearch.java.html</a> for Algorithms textbook.</p>

<pre class="lang-java prettyprint-override"><code>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 &lt;= hi) {
            // Key is in a[lo..hi] or not present.
            int mid = lo + (hi - lo) / 2;
            if      (key &lt; a[mid]) hi = mid - 1;
            else if (key &gt; 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);
        }
    }
}
</code></pre>

<p>I get this error</p>

<pre><code>$ 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
</code></pre>
