Question

I’m trying to compile the following code:

package week1;

public class ThreeSum {
    public static int count(int[] a) {
        // count triples that sum to 0
        int count = 0;
        for (int i = 0; i<a.length; i++) {
            for (int j = i+1; j < a.length; j++) {
                for (int k = j+1; k < a.length; k++) {
                    if (a[i] + a[j] + a[k] == 0) {
                        count++;
                    }
                }
            }
        }
        return count;
    }

    public static void main(String[] args) {
        int[] a = In.readInts(args[0]);
        StdOut.println(count(a));
    }
}

This code is in the ThreeSum.java file in week1 folder. Both classes “In” and “StdOut” are in the package stdlib.jar which is in the ./lib folder.
I’ve always used an IDE and now decided to use a command line. So on my

javac -cp .:lib/stdlib.jar week1/ThreeSum.java

and other variants of classpath parameters it returns an error:

week1\ThreeSum.java:20: error: cannot find symbol
        int[] a = In.readInts(args[0]);
                  ^
  symbol:   variable In
  location: class ThreeSum

week1\ThreeSum.java:21: error: cannot find symbol
        StdOut.println(count(a));
        ^
  symbol:   variable StdOut
  location: class ThreeSum

How a proper -cp option should look like in my case?

Answer 1

What are In and StdOut? There are no such classes in the JDK. You do have System.in and System.out. Please see the Java docs.

There’s no readInts() method on System.in. Perhaps you mean some custom classes of your own.

Write it like this and forget about that JAR dependency:

package week1;

/**
 * ThreeSum
 * @author mduffy
 * @since 8/14/12 1:53 PM
 * @link http://stackoverflow.com/questions/11950145/cant-correctly-setup-classpath#comment15924351_11950145
 */
public class ThreeSum {
    public static int count(int[] a) {
        // count triples that sum to 0
        int count = 0;
        for (int i = 0; i<a.length; i++) {
            for (int j = i+1; j < a.length; j++) {
                for (int k = j+1; k < a.length; k++) {
                    if (a[i] + a[j] + a[k] == 0) {
                        count++;
                    }
                }
            }
        }
        return count;
    }

    public static void main(String[] args) {
        int[] values = new int[args.length];
        int valuesCount = 0;
        for (String arg : args) {
            int value = Integer.valueOf(arg);
            values[valuesCount++] = value;
        }
        System.out.println(String.format("count: %d", count(values)));
    }
}