add maven as package manager

add ShowObjectHeader.java to show object header

.idea/compiler.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <annotationProcessing>
+      <profile name="Maven default annotation processors profile" enabled="true">
+        <sourceOutputDir name="target/generated-sources/annotations" />
+        <sourceTestOutputDir name="target/generated-test-sources/test-annotations" />
+        <outputRelativeToContentRoot value="true" />
+        <module name="java_test" />
+      </profile>
+    </annotationProcessing>
+    <bytecodeTargetLevel target="21" />
+  </component>
+</project>

.idea/inspectionProfiles/Project_Default.xml

@@ -0,0 +1,8 @@
+<component name="InspectionProjectProfileManager">
+  <profile version="1.0">
+    <option name="myName" value="Project Default" />
+    <inspection_tool class="AutoCloseableResource" enabled="true" level="WARNING" enabled_by_default="true">
+      <option name="METHOD_MATCHER_CONFIG" value="java.util.Formatter,format,java.io.Writer,append,com.google.common.base.Preconditions,checkNotNull,org.hibernate.Session,close,java.io.PrintWriter,printf,java.io.PrintStream,printf,java.lang.foreign.Arena,ofAuto,java.lang.foreign.Arena,global,java.util.concurrent.Executors,newFixedThreadPool" />
+    </inspection_tool>
+  </profile>
+</component>

.idea/jarRepositories.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RemoteRepositoriesConfiguration">
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Maven Central repository" />
+      <option name="url" value="https://repo1.maven.org/maven2" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="jboss.community" />
+      <option name="name" value="JBoss Community repository" />
+      <option name="url" value="https://repository.jboss.org/nexus/content/repositories/public/" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Central Repository" />
+      <option name="url" value="https://maven.aliyun.com/repository/central" />
+    </remote-repository>
+  </component>
+</project>

.idea/misc.xml

@@ -1,5 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
   <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="21" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
   </component>

java_test.iml

@@ -1,11 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <module type="JAVA_MODULE" version="4">
-  <component name="NewModuleRootManager" inherit-compiler-output="true">
-    <exclude-output />
-    <content url="file://$MODULE_DIR$">
+  <component name="AdditionalModuleElements">
+    <content url="file://$MODULE_DIR$" dumb="true">
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
     </content>
-    <orderEntry type="inheritedJdk" />
-    <orderEntry type="sourceFolder" forTests="false" />
   </component>
 </module>

pom.xml

@@ -0,0 +1,38 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.kuaslab</groupId>
+    <artifactId>java-learning</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.openjdk.jol</groupId>
+            <artifactId>jol-core</artifactId>
+            <version>0.17</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.1</version>
+                <configuration>
+                    <source>{maven.compiler.source}</source>
+                    <target>{maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

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.*;