113 lines
1.8 KiB
Markdown
113 lines
1.8 KiB
Markdown
###### 1. Integer[]转[ArrayList](https://so.csdn.net/so/search?q=ArrayList&spm=1001.2101.3001.7020)
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(1) 方法一：
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利用[Arrays工具类](https://blog.csdn.net/k909397116/article/details/107308897)中的`asList`方法
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```Java
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Integer[] arr = {1,2,3};
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ArrayList<Integer> list = new ArrayList<>(Arrays.asList(arr));
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12
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12
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```
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(2) 方法二：
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利用Collections工具类中的`addAll`方法
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```Java
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Integer[] arr = {1,2,3};
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ArrayList<Integer> list = new ArrayList<>(array.length);
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Collections.addAll(list, arr);
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123
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123
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```
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(3) 注意：
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Java中集合只能存放引用数据类型，在使用`asList`或`addAll`方法时，被转换的[数组](https://so.csdn.net/so/search?q=%E6%95%B0%E7%BB%84&spm=1001.2101.3001.7020)必须是存放引用数据类型的数组，如果是基本数据类型数组请在转换前先把其转换为对应的[包装类型](https://blog.csdn.net/k909397116/article/details/107323121)数组，下面会介绍。
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###### 2. ArrayList转Integer[]
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```Java
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ArrayList<Integer> list = new ArrayList<>();
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Integer[] arr = list.toArray(new Integer[0]);
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12
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12
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```
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## 二、Integer[]与int[]互转
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---
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###### 1. Integer[]转int[]
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```Java
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Integer[] arr1 = {1,2,3};
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int[] arr2 = Arrays.stream(arr1).mapToInt(Integer::valueOf).toArray();
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12
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12
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```
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###### 2. int[]转Integer[]
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```Java
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int[] arr1 = {1,2,3};
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Integer[] arr2 = Arrays.stream(arr1).boxed().toArray(Integer[]::new);
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12
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12
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```
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## 三、int[]与ArrayList的互转
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---
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###### 1. int[]转ArrayList
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```Java
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int[] arr = {1,2,3};
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List<Integer> list = Arrays.stream(arr).boxed().collect(Collectors.toList());
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12
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12
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```
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###### 2. ArrayList转int[]
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```Java
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ArrayList<Integer> list = new ArrayList<>();
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int[] arr = list.stream().mapToInt(Integer::valueOf).toArray();
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```
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