ArrayList<Double> ar = new ArrayList<>();

回答: 根据提供的引用内容，ArrayList<Double> ar = new ArrayList<>();是创建了一个ArrayList集合，其中的元素类型为Double。这个ArrayList可以存储Double类型的数据。
#### 引用[.reference_title]
- *1* [Java中ArrayList的基础学习](https://blog.csdn.net/weixin_45414884/article/details/96744538)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^control_2,239^v3^insert_chatgpt"}} ] [.reference_item]
- *2* *3* [Java中的Collections类](https://blog.csdn.net/zzzzlei123123123/article/details/96011167)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^control_2,239^v3^insert_chatgpt"}} ] [.reference_item]
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