update 204

Author: fishercoder1534

Diff for: src/main/java/com/fishercoder/solutions/firstthousand/_204.java

@@ -2,14 +2,20 @@
 
 public class _204 {
     public static class Solution1 {
+        /**
+         * Reference: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+         * This is an ancient algorithm to efficiently count the number of primes up to a given point:
+         * it does so iteratively by marking composite (i.e. not prime) the multiples of each prime,
+         * starting from 2, then all remaining ones are prime.
+         */
         public int countPrimes(int n) {
-            boolean[] notPrime = new boolean[n];
+            boolean[] notPrimes = new boolean[n];
             int count = 0;
             for (int i = 2; i < n; i++) {
-                if (!notPrime[i]) {
+                if (!notPrimes[i]) {
                     count++;
                     for (int j = 2; i * j < n; j++) {
-                        notPrime[i * j] = true;
+                        notPrimes[i * j] = true;
                     }
                 }
             }

Diff for: src/test/java/com/fishercoder/firstthousand/_204Test.java

@@ -1,16 +1,16 @@
 package com.fishercoder.firstthousand;
 
 import com.fishercoder.solutions.firstthousand._204;
-import org.junit.BeforeClass;
-import org.junit.Test;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
-import static org.junit.Assert.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 public class _204Test {
     private static _204.Solution1 solution1;
 
-    @BeforeClass
-    public static void setup() {
+    @BeforeEach
+    public void setup() {
         solution1 = new _204.Solution1();
     }