BAEL-1077 Guide to volatile keyword (#2433)

* review changes

* BAEL-1024 Removed the proxy reference

* BAEL-1024 Renamed methods

* BAEL-1077 Guide to volatile keyword

core-java/src/main/java/com/baeldung/concurrent/volatilekeyword/SharedObject.java

@@ -0,0 +1,13 @@
+package com.baeldung.concurrent.volatilekeyword;
+
+
+public class SharedObject {
+    private volatile int count=0;
+
+    public void increamentCount(){
+        count++;
+    }
+    public int  getCount(){
+        return count;
+    }
+}

core-java/src/test/java/com/baeldung/concurrent/volatilekeyword/SharedObjectManualTest.java

@@ -0,0 +1,99 @@
+package com.baeldung.concurrent.volatilekeyword;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import static junit.framework.Assert.assertEquals;
+
+public class SharedObjectManualTest {
+
+    SharedObject sharedObject;
+    int valueReadByThread2;
+    int valueReadByThread3;
+
+    @Before
+    public void setUp(){
+        sharedObject = new SharedObject();
+    }
+
+    @Test
+    public void whenOneThreadWrites_thenVolatileReadsFromMainMemory() throws InterruptedException {
+        Thread writer = new Thread(){
+            public void run(){
+                sharedObject.increamentCount();
+            }
+        };
+        writer.start();
+
+
+        Thread readerOne = new Thread(){
+            public void run(){
+                try {
+                    Thread.sleep(1000);
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
+                valueReadByThread2= sharedObject.getCount();
+            }
+        };
+        readerOne.start();
+
+        Thread readerTwo = new Thread(){
+            public void run(){
+                try {
+                    Thread.sleep(1000);
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
+                valueReadByThread3=sharedObject.getCount();
+            }
+        };
+        readerTwo.start();
+
+        assertEquals(1,valueReadByThread2);
+        assertEquals(1,valueReadByThread3);
+
+    }
+
+    @Test
+    public void whenTwoThreadWrites_thenVolatileReadsFromMainMemory() throws InterruptedException {
+        Thread writerOne = new Thread(){
+            public void run(){
+                sharedObject.increamentCount();
+            }
+        };
+        writerOne.start();
+        Thread.sleep(100);
+
+        Thread writerTwo = new Thread(){
+            public void run(){
+                sharedObject.increamentCount();
+            }
+        };
+        writerTwo.start();
+        Thread.sleep(100);
+
+        Thread readerOne = new Thread(){
+            public void run(){
+                valueReadByThread2= sharedObject.getCount();
+            }
+        };
+        readerOne.start();
+
+        Thread readerTwo = new Thread(){
+            public void run(){
+                valueReadByThread3=sharedObject.getCount();
+            }
+        };
+        readerTwo.start();
+
+        assertEquals(2,valueReadByThread2);
+        assertEquals(2,valueReadByThread3);
+
+    }
+    @After
+    public void cleanup(){
+        sharedObject = null;
+    }
+}