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Java语言中的集合/基于 "Eratosthenes 方法" 对 C++ 和 Java 的性能测试/Sieve.java

+import java.util.*;
+
+/**
+ * This program runs the Sieve of Eratosthenes benchmark. It computes all primes
+ * up to 2,000,000.
+ *
+ * @author Cay Horstmann
+ * @version 1.21 2004-08-03
+ */
+
+public class Sieve {
+   public static void main(String[] s) {
+      int n = 2000000;
+      long start = System.currentTimeMillis();
+      BitSet b = new BitSet(n + 1);
+      int count = 0;
+      int i;
+      for (i = 2; i <= n; i++)
+         b.set(i);
+      i = 2;
+      while (i * i <= n) {
+         if (b.get(i)) {
+            count++;
+            int k = 2 * i;
+            while (k <= n) {
+               b.clear(k);
+               k += i;
+            }
+         }
+         i++;
+      }
+      while (i <= n) {
+         if (b.get(i))
+            count++;
+         i++;
+      }
+      long end = System.currentTimeMillis();
+      System.out.println(count + " primes");
+      System.out.println((end - start) + " milliseconds");
+   }
+}