我怎样才能把这个数组变成一个做同样事情的ArrayList? [英] How can I turn this array into an ArrayList that does the same thing?

问题描述

我想把这个程序的数组变成ArrayList.到目前为止，我知道该数组将变为

I want to make turn this program's array into an ArrayList. So far I know that the array will turn into

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

，每个列表[i]都会变成:

and that each list[i] will turn into:

list.get(i)

但是我不确定以下行将满足ArrayList版本

however I am not sure what the following line will be in order to satisfy the ArrayList version

list[i] = new StudentList();

所以这是完整的代码:

public static void main(String[] args) {

    StudentList[] list = new StudentList[5];

    int i;

    for (i = 0; i < list.length; ++i) {

        list[i] = new StudentList();

        System.out.println("\nEnter information of Student _" + (i + 1) + "\n");
        list[i].DataUserPrompt();

    }
    for (i = 0; i < list.length; ++i) {

        list[i].DisplayStudentData();
    }

    File file12 = new File("s_records.txt");

    try {

        PrintWriter output = new PrintWriter(file12);

        output.close();

    } catch (IOException e) {
        e.printStackTrace();
    }
}

推荐答案

new StudentList[5]是大小为5的数组，所有值均为null，因此您可以使用new StudentList()创建5个对象并将其分配给5个数组索引

new StudentList[5] is an array of size 5, with all values null, so you create 5 objects using new StudentList() and assign to the 5 array indexes.

但是，new ArrayList()创建一个空列表(大小为0).请注意，new ArrayList(5)还会创建一个空列表，它刚刚进行了优化以存储5个元素.因此，您需要创建并添加 5个对象:

However, new ArrayList() creates an empty list (size 0). Note that new ArrayList(5) also creates an empty list, it is just optimized to store 5 elements. So you need to create and add 5 objects:

List<StudentList> list = new ArrayList<>();
for (int i = 0; i < 5; i++) {
    list.add(new StudentList());
}

以上等同于数组代码:

StudentList[] list = new StudentList[5];
for (int i = 0; i < 5; i++) {
    list[i] = new StudentList();
}

在这两种情况下，最终的大小都是5的list，其中包含5个对象.

In both cases you end up with a list of size 5, with 5 objects.

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