arraylist<integer>

ArrayList<Integer> 是 Java 中的一种数据类型，表示一个动态数组，其中存储了多个整数。ArrayList 类是 Java 的一种集合类，支持动态增长，可以方便地存储、检索和删除数据。

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ArrayList<Integer>

An ArrayList is a class in Java that provides a dynamic array implementation. It is part of the Java Collections Framework and is used to store a collection of objects. The ArrayList class is a generic class that can be used to store objects of any type.

The ArrayList<Integer> denotes an ArrayList that can only store objects of the Integer type. This is achieved through the use of Java generics, which allows the type of objects stored in a collection to be specified at compile time.

Here's an example of how to create an ArrayList<Integer>:

ArrayList<Integer> myList = new ArrayList<Integer>();

This creates a new ArrayList that can store objects of the Integer type. The ArrayList is initially empty, and elements can be added using the `add()` method:

myList.add(1);
myList.add(2);
myList.add(3);

This adds the integers 1, 2, and 3 to the ArrayList. The `size()` method can be used to get the number of elements in the ArrayList:

int size = myList.size(); // size is now 3

Elements can be retrieved from the ArrayList using the `get()` method:

int element = myList.get(0); // element is now 1

This retrieves the first element in the ArrayList (at index 0) and stores it in the `element` variable.

下列集合对象创建正确的是（） ArrayList<int> list = new ArrayList<>(); ArrayList<Integer> list = new ArrayList<>(); ArrayList<> list = new ArrayList<Integer>(); ArrayList<Object> list4 = new ArrayList<Integer>();

下列集合对象创建正确的是：

ArrayList<Integer> list = new ArrayList<>();

在Java中，泛型只能使用引用类型，不能使用基本类型。因此，需要使用包装类Integer来代替基本类型int。正确的语法是在尖括号内指定泛型的类型，如ArrayList<Integer>表示创建一个存储Integer对象的ArrayList集合对象。

其他选项是错误的：

ArrayList<int> list = new ArrayList<>(); - 错误，基本类型int不能用作泛型参数。

ArrayList<> list = new ArrayList<Integer>(); - 错误，尖括号内必须指定泛型的类型。

ArrayList<Object> list4 = new ArrayList<Integer>(); - 错误，泛型类型必须匹配，不能将一个泛型类的对象赋值给另一个泛型类的引用。