Add instructions, comments to Average and Print Evens

Clarified instructions, added main method for students
to test their methods. Also deleted method blocks
so that students can practice declaring methods.
Also deleted JavaDoc comments to let students
practice writing JavaDoc comments.

Author: phrdang

src/com/codefortomorrow/intermediate/chapter11/practice/Average.java

@@ -1,16 +1,24 @@
 package com.codefortomorrow.intermediate.chapter11.practice;
 
+/*
+Code a method called average that takes
+two double parameters, a and b.
+The method should return the average
+of the two doubles.
+
+Test if your average method works in the
+main method by calling it at least 3 times
+with different arguments and printing the results.
+
+Bonus points if you write a JavaDoc comment for
+the average() method.
+*/
+
 public class Average {
 
-    /**
-     * Difficulty: 1
-     *
-     * Returns the average of two doubles
-     * @param a the first double
-     * @param b the second double
-     * @return average
-     */
-    public static double average(double a, double b) {
-        return 0.0; // TODO: Fix!
+    public static void main(String[] args) {
+        // Test your average method here
     }
+
+    // Write your average method here
 }

src/com/codefortomorrow/intermediate/chapter11/practice/PrintEvens.java

@@ -1,15 +1,22 @@
 package com.codefortomorrow.intermediate.chapter11.practice;
 
+/*
+Code a method printEvens that takes an integer parameter n.
+The method should print the first n even numbers to the console.
+(Note that 0 is considered an even number.)
+
+Test if your printEvens method works in the main method
+by calling it at least 3 times with different arguments.
+
+Bonus points if you write a JavaDoc comment
+for the printEvens method.
+*/
+
 public class PrintEvens {
 
-    /**
-     * Difficulty: 1
-     *
-     * Print the first n even integers
-     * (consider 0 an even number)
-     * @param n number of even integers to print
-     */
-    public static void printEvens(int n) {
-        // write code here
+    public static void main(String[] args) {
+        // Test your printEvens method here
     }
+
+    // Write your printEvens method here
 }

src/com/codefortomorrow/intermediate/chapter11/solutions/Average.java

@@ -1,14 +1,33 @@
 package com.codefortomorrow.intermediate.chapter11.solutions;
 
+/*
+Code a method called average that takes
+two double parameters, a and b.
+The method should return the average
+of the two doubles.
+
+Test if your average method works in the
+main method by calling it at least 3 times
+with different arguments and printing the results.
+
+Bonus points if you write a JavaDoc comment for
+the average() method.
+*/
+
 public class Average {
 
+    public static void main(String[] args) {
+        // test the average method
+        System.out.println(average(5, 4)); // prints 4.5
+        System.out.println(average(0, 10)); // prints 5.0
+        System.out.println(average(1.5, 3.75)); // prints 2.625
+    }
+
     /**
-     * Difficulty: 1
-     *
      * Returns the average of two doubles
      * @param a the first double
      * @param b the second double
-     * @return average
+     * @return the average of two doubles
      */
     public static double average(double a, double b) {
         return (a + b) / 2;

src/com/codefortomorrow/intermediate/chapter11/solutions/PrintEvens.java

@@ -1,23 +1,52 @@
 package com.codefortomorrow.intermediate.chapter11.solutions;
 
+/*
+Code a method printEvens that takes an integer parameter n.
+The method should print the first n even numbers to the console.
+(Note that 0 is considered an even number.)
+
+Test if your printEvens method works in the main method
+by calling it at least 3 times with different arguments.
+
+Bonus points if you write a JavaDoc comment
+for the printEvens method.
+*/
+
 public class PrintEvens {
 
+    public static void main(String[] args) {
+        // test printEvens method
+        printEvens(5); // prints 0 2 4 6 8
+        printEvens(10); // prints 0 2 4 6 8 10 12 14 16 18
+        printEvens(0); // prints nothing
+    }
+
     /**
-     * Difficulty: 2
-     *
-     * Print the first n even integers
-     * (consider 0 an even number)
-     * @param n number of even integers to print
+     * Prints the first n even integers
+     * @param n  number of even integers to print
      */
     public static void printEvens(int n) {
-        int evens = 0;
-        int i = 0;
+        int evens = 0; // number of evens printed
+        int i = 0; // current number
         while (evens < n) {
+            // if current number is even, print it
             if (i % 2 == 0) {
                 System.out.print(i + " ");
                 evens++;
             }
             i++;
         }
+        System.out.println(); // move cursor to next line
+
+        // alternate solution using for loop
+        // int numberOfEvensPrinted = 0;
+        // for (int num = 0; numberOfEvensPrinted < n; num++) {
+        //     // if the number is even, print it
+        //     if (num % 2 == 0) {
+        //         System.out.print(num + " ");
+        //         numberOfEvensPrinted++;
+        //     }
+        // }
+        // System.out.println(); // move cursor to next line
     }
 }