add maven as package manager

add ShowObjectHeader.java to show object header

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

@@ -0,0 +1,18 @@
+package main.java.jvm.createthread;
+
+public class CreateByThreadGroup {
+
+    public static void main(String[] args) {
+        ThreadGroup threadGroup = new ThreadGroup("threadGroup");
+
+        new Thread(threadGroup, () -> {
+            System.out.println("6-T1......");
+        },"T1").start();
+        new Thread(threadGroup, () -> {
+            System.out.println("6-T2......");
+        },"T2").start();
+        new Thread(threadGroup, () -> {
+            System.out.println("6-T3......");
+        },"T3").start();
+    }
+}