Offer code improvement suggestions

I'm trying to migrate from IntelliJ and one of the best features it has is the code improvement suggestions. For example, if I'm using JDK7+ and my code is not using the "diamond operator", it offers me to convert the code to this cleaner version. And it does this for:

1. Convert to try-with-resources on JDK7+
2. Convert to lambda on JDK8+

And a lot more.

I know this issue is very broad and probably each of theses code refactoring should have its own issue linked to this one. But first I want to check what the core developers think of this.

该 issue 未指定文件、测试或入口点，并提出了一系列范围广泛的 Java 重构。首先审查项目现有的代码改进能力以及每项所请求转换的范围；done 应定义为一个或多个分别限定范围的建议，并明确 JDK 版本行为和测试。