diff --git a/docs/book/24-Concurrent-Programming.md b/docs/book/24-Concurrent-Programming.md
index 0a85cee..603eb9e 100644
--- a/docs/book/24-Concurrent-Programming.md
+++ b/docs/book/24-Concurrent-Programming.md
@@ -771,7 +771,7 @@ Java并发的历史始于非常原始和有问题的机制，并且充满了各
 // concurrent/NapTask.java
 import onjava.Nap;
 public class NapTask implements Runnable {
-    finalint id;
+    final int id;
     public NapTask(int id) {
         this.id = id;
         }