Update Java 基础.md

更新两条参考资料的链接，已下线的文章注明。

notes/Java 基础.md

@@ -1993,13 +1993,13 @@ Blank.java:1: 错误: 可能尚未初始化变量x
 - [StackOverflow : Why don't Java's +=, -=, *=, /= compound assignment operators require casting?](https://stackoverflow.com/questions/8710619/why-dont-javas-compound-assignment-operators-require-casting)
 - [StackOverflow : Why can't your switch statement data type be long, Java?](https://stackoverflow.com/questions/2676210/why-cant-your-switch-statement-data-type-be-long-java)
 - [Abstract Methods and Classes](https://docs.oracle.com/javase/tutorial/java/IandI/abstract.html)
-- [深入理解 abstract class 和 interface](https://www.ibm.com/developerworks/cn/java/l-javainterface-abstract/)
+- 深入理解 abstract class 和 interface（IBM developerWorks 中文站，已下线）
 - [When to Use Abstract Class and Interface](https://dzone.com/articles/when-to-use-abstract-class-and-intreface)
-- [Java 9 Private Methods in Interfaces](https://www.journaldev.com/12850/java-9-private-methods-interfaces)
+- [Java 9 Features with Examples](https://www.digitalocean.com/community/tutorials/java-9-features-with-examples)
 - [Using the Keyword super](https://docs.oracle.com/javase/tutorial/java/IandI/super.html)
 - [Trail: The Reflection API](https://docs.oracle.com/javase/tutorial/reflect/index.html)
 - [深入解析 Java 反射（1）- 基础](http://www.sczyh30.com/posts/Java/java-reflection-1/)
-- [Java Exception Interview Questions and Answers](https://www.journaldev.com/2167/java-exception-interview-questions-and-answers)
+- [Java Exception Interview Questions and Answers](https://www.digitalocean.com/community/tutorials/java-exception-interview-questions-and-answers)
 - [Java提高篇——Java 异常处理](https://www.cnblogs.com/Qian123/p/5715402.html)
 - [Java 泛型详解](https://www.cnblogs.com/Blue-Keroro/p/8875898.html)
 - [10 道 Java 泛型面试题](https://cloud.tencent.com/developer/article/1033693)