#6 -- using AtomicInteger instead of primitive int to track invocatio…

…ns of the BooleanGenerator, just in case the generators are not thread-safe -- not entirely sure, but not a bad way to think anyhow IMHO.

src/main/java/com/pholser/junit/quickcheck/generator/BooleanGenerator.java

@@ -25,12 +25,14 @@ a copy of this software and associated documentation files (the
 
 package com.pholser.junit.quickcheck.generator;
 
+import java.util.concurrent.atomic.AtomicInteger;
+
 import com.pholser.junit.quickcheck.internal.random.SourceOfRandomness;
 
 import static java.util.Arrays.*;
 
 public class BooleanGenerator extends Generator<Boolean> {
-    private int invocations;
+    private final AtomicInteger invocations = new AtomicInteger(0);
 
     @SuppressWarnings("unchecked")
     public BooleanGenerator() {
@@ -39,6 +41,6 @@ public BooleanGenerator() {
 
     @Override
     public Boolean generate(SourceOfRandomness random, int size) {
-        return ++invocations % 2 == 0;
+        return invocations.incrementAndGet() % 2 == 0;
     }
 }