diff --git a/src/main/java/com/iflytop/uf/UfCommand.java b/src/main/java/com/iflytop/uf/UfCommand.java
new file mode 100644
index 0000000..99c9957
--- /dev/null
+++ b/src/main/java/com/iflytop/uf/UfCommand.java
@@ -0,0 +1,6 @@
+package com.iflytop.uf;
+import java.util.List;
+public interface UfCommand {
+    // execute
+    void execute( List<String> args );
+}
diff --git a/src/main/java/com/iflytop/uf/command/UfCmdDelay.java b/src/main/java/com/iflytop/uf/command/UfCmdDelay.java
new file mode 100644
index 0000000..1d94ccf
--- /dev/null
+++ b/src/main/java/com/iflytop/uf/command/UfCmdDelay.java
@@ -0,0 +1,16 @@
+package com.iflytop.uf.command;
+import com.iflytop.uf.UfCommand;
+import java.util.List;
+public class UfCmdDelay implements UfCommand {
+    @Override
+    public void execute( List<String> args ) {
+        // get delay time
+        int delayTime = Integer.parseInt(args.get(0));
+        // sleep
+        try {
+            Thread.sleep(delayTime);
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}