add maven as package manager

add ShowObjectHeader.java to show object header

src/main/java/jvm/ObjectCreate.java

@@ -1,7 +1,7 @@
-package jvm;
+package main.java.jvm;
 
 /**
- * This class is intended to demo how jvm create object and invoke constructor. Please see byte code.
+ * This class is intended to demo how main.java.jvm create object and invoke constructor. Please see byte code.
  * use javap -v ObjectCreate.class  or javap -c  ObjectCreate.class to see byte code
  */
 public class ObjectCreate {

src/main/java/jvm/ShowObjectHeader.java

@@ -0,0 +1,42 @@
+package jvm;
+
+import org.openjdk.jol.info.ClassLayout;
+
+public class ShowObjectHeader {
+
+    static final Object lock = new Object();
+
+    public void syncObject() {
+        synchronized (lock) {
+            try {
+                Thread.sleep(1000);
+                System.out.println("enter sync");
+                System.out.println(ClassLayout.parseInstance(lock).toPrintable());
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+
+    public static void main(String[] args) throws InterruptedException {
+        ShowObjectHeader showObjectHeader = new ShowObjectHeader();
+        System.out.println("newly created");
+        System.out.println(ClassLayout.parseInstance(lock).toPrintable());
+
+        Thread t1 = new Thread(showObjectHeader::syncObject);
+        t1.start();
+        t1.join();
+
+        Thread t2 = new Thread(showObjectHeader::syncObject);
+        Thread t3 = new Thread(showObjectHeader::syncObject);
+
+        t2.start();
+        t3.start();
+
+        t2.join();
+        t3.join();
+        System.out.println("after sync");
+        System.out.println(ClassLayout.parseInstance(lock).toPrintable());
+
+    }
+}

src/main/java/jvm/createthread/CreateByAnonymousClass.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 public class CreateByAnonymousClass {
 

src/main/java/jvm/createthread/CreateByCallable.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 import java.util.concurrent.Callable;
 import java.util.concurrent.FutureTask;

src/main/java/jvm/createthread/CreateByCompletableFuture.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;

src/main/java/jvm/createthread/CreateByExecutorService.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 import java.util.concurrent.*;
 

src/main/java/jvm/createthread/CreateByForkJoin.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 import java.util.Arrays;
 import java.util.List;

src/main/java/jvm/createthread/CreateByFutureTask.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 import java.util.concurrent.FutureTask;
 

src/main/java/jvm/createthread/CreateByRunnable.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 public class CreateByRunnable implements Runnable{
     @Override

src/main/java/jvm/createthread/CreateByThread.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 public class CreateByThread extends Thread{
     @Override

src/main/java/jvm/createthread/CreateByThreadGroup.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 public class CreateByThreadGroup {
 

src/main/java/jvm/createthread/CreateByTimer.java

@@ -1,4 +1,4 @@
-package createthread;
+package main.java.jvm.createthread;
 
 import java.util.Timer;
 import java.util.TimerTask;

src/main/java/recursive/TreeNode.java

@@ -1,4 +1,4 @@
-package recursive;
+package main.java.recursive;
 
 import java.util.ArrayList;
 import java.util.List;

src/main/java/recursive/TreeStructure.java

@@ -1,4 +1,4 @@
-package recursive;
+package main.java.recursive;
 
 import java.util.*;