fix multiple annotations npe

Mike Liu · web-flow · commit 0a38f722c183 · 2021-04-18T18:53:20.000+08:00
Hints annotation needs add @retention(RetentionPolicy.RUNTIME), otherwise it will throw npe.
diff --git a/docs/java/new-features/Java8新特性总结.md b/docs/java/new-features/Java8新特性总结.md
@@ -872,6 +872,7 @@ System.out.println(string);     // Nov 03, 2014 - 07:13
 首先定义一个包装类Hints注解用来放置一组具体的Hint注解：
 
 ```java
+@Retention(RetentionPolicy.RUNTIME)
 @interface Hints {
     Hint[] value();
 }

Original file line number	Diff line number	Diff line change
`@@ -872,6 +872,7 @@ System.out.println(string); // Nov 03, 2014 - 07:13`
`872`	`872`	`首先定义一个包装类Hints注解用来放置一组具体的Hint注解：`
`873`	`873`
`874`	`874`	```java
	`875`	`+@Retention(RetentionPolicy.RUNTIME)`
`875`	`876`	`@interface Hints {`
`876`	`877`	`Hint[] value();`
`877`	`878`	`}`