diff --git a/.gitignore b/.gitignore
index f68d109..9211a32 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,4 +26,5 @@ bin/
 .vscode/
 
 ### Mac OS ###
-.DS_Store
\ No newline at end of file
+.DS_Store
+/.idea/
diff --git a/src/main/java/jvm/debugtool/DeadLockDemo.java b/src/main/java/jvm/debugtool/DeadLockDemo.java
new file mode 100644
index 0000000..25e7171
--- /dev/null
+++ b/src/main/java/jvm/debugtool/DeadLockDemo.java
@@ -0,0 +1,36 @@
+package jvm.debugtool;
+
+/**
+ * debug tool: Jconsole
+ */
+public class DeadLockDemo{
+    static class SyncAddRunnable implements Runnable {
+        int a, b;
+
+        public SyncAddRunnable(int a, int b) {
+            this.a = a;
+            this.b = b;
+        }
+
+        @Override
+        public void run() {
+            synchronized (Integer.valueOf(a)) {
+                try {
+                    Thread.sleep(100);
+                } catch ( InterruptedException e) {
+                    e.printStackTrace();
+                }
+                synchronized (Integer.valueOf(b)) {
+                    System.out.println(a + b);
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        for(int i = 0;i < 100;i++){
+            new Thread(new SyncAddRunnable(1,2)).start();
+            new Thread(new SyncAddRunnable(2,1)).start();
+        }
+    }
+}
diff --git a/src/main/java/jvm/debugtool/JHSDBTestCase.java b/src/main/java/jvm/debugtool/JHSDBTestCase.java
new file mode 100644
index 0000000..d5cd831
--- /dev/null
+++ b/src/main/java/jvm/debugtool/JHSDBTestCase.java
@@ -0,0 +1,26 @@
+package jvm.debugtool;
+
+/**
+ * vm args: -Xmx10m -XX:+UseSerialGC -XX:-UseCompressedOops
+ */
+public class JHSDBTestCase {
+
+    static class  Test {
+        static  ObjectHolder staticObj = new ObjectHolder();
+
+        ObjectHolder instanceObj = new ObjectHolder();
+
+        void foo() {
+            ObjectHolder localObj = new ObjectHolder();
+            //set break point here
+            System.out.println("done");
+        }
+    }
+
+    private static class ObjectHolder {}
+
+    public static void main(String[] args) {
+        Test test = new JHSDBTestCase.Test();
+        test.foo();
+    }
+}