optimized memory used

src/test/java/com/alibaba/druid/stat/PerfTest.java

@@ -0,0 +1,56 @@
+package com.alibaba.druid.stat;
+
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicLongFieldUpdater;
+
+import junit.framework.TestCase;
+
+public class PerfTest extends TestCase {
+
+    public void test_0() throws Exception {
+        for (int i = 0; i < 3; ++i) {
+            long startMillis = System.currentTimeMillis();
+            a();
+            long millis = System.currentTimeMillis() - startMillis;
+            System.out.println("a : " + millis);
+        }
+    }
+
+    private void a() {
+        A a = new A();
+        for (int i = 0; i < 1000 * 1000 * 1000; ++i) {
+            a.incrementAndGet();
+        }
+    }
+
+    private void b() {
+        B b = new B();
+        for (int i = 0; i < 1000 * 1000 * 1000; ++i) {
+            b.incrementAndGet();
+        }
+    }
+
+    public static class A {
+
+        private volatile long                  value;
+
+        static final AtomicLongFieldUpdater<A> updater = AtomicLongFieldUpdater.newUpdater(A.class, "value");
+
+        public long incrementAndGet() {
+            return updater.incrementAndGet(this);
+        }
+
+        public long getValue() {
+            return value;
+        }
+    }
+
+    public static class B {
+
+        private final AtomicLong value = new AtomicLong();
+
+        public long incrementAndGet() {
+            return value.incrementAndGet();
+        }
+    }
+}