BAEL-1029 - deep20jain@gmail.com - An Introduction to Atomic Variables in Java (#2269)

* Adding test classes for java atomic variables

* Updating counter with atomic integer

* Adding reason for ignoring test

core-java/src/main/java/com/baeldung/concurrent/atomic/SafeCounterWithLock.java

@@ -0,0 +1,13 @@
+package com.baeldung.concurrent.atomic;
+
+public class SafeCounterWithLock {
+    int counter;
+    
+    public int getValue() {
+        return counter;
+    }
+    
+    public synchronized void increment() {
+        counter++;
+    }
+}

core-java/src/main/java/com/baeldung/concurrent/atomic/SafeCounterWithoutLock.java

@@ -0,0 +1,21 @@
+package com.baeldung.concurrent.atomic;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class SafeCounterWithoutLock {
+    AtomicInteger counter = new AtomicInteger(0);
+    
+    public int getValue() {
+        return counter.get();
+    }
+    
+    public void increment() {
+        while(true) {
+            int existingValue = getValue();
+            int newValue = existingValue + 1;
+            if(counter.compareAndSet(existingValue, newValue)) {
+                return;
+            }
+        }
+    }
+}

core-java/src/main/java/com/baeldung/concurrent/atomic/UnsafeCounter.java

@@ -0,0 +1,13 @@
+package com.baeldung.concurrent.atomic;
+
+public class UnsafeCounter {
+    int counter;
+    
+    public int getValue() {
+        return counter;
+    }
+    
+    public void increment() {
+        counter++;
+    }
+}