具有相同值的项目清单 [英] List of items with same values

问题描述

我正在从文件中创建项目列表

BufferedReader reader = new BufferedReader(
    new InputStreamReader(new FileInputStream("H:/temp/data.csv")));
try {
    List<Item> items = new ArrayList<Item>();
    Item item = new Item();

    String line = null;
    while ((line = reader.readLine()) != null) {
        String[] split = line.split(",");

        item.name = split[0];
        item.quantity = Integer.valueOf(split[1]);
        item.price = Double.valueOf(split[2]);
        item.total = item.quantity * item.price;

        items.add(item);
    }

    for (Item item2 : items) {
        System.out.println("Item: " + item2.name);
    }
} catch (IOException e) {
    reader.close();

    e.printStackTrace();
}

问题是列表显示文件的最后一行作为所有项目的值.

解决方案

您的代码存在的问题是，您仅创建了一个Item Object(Item item = new Item)实例，并且同一实例一次又一次地添加到列表中./p>

您需要为文件中的每一行创建Item的新实例，并将其添加到列表中，如下所示.

修复:

List<Item> items = new ArrayList<Item>();

String line = null;
while ((line = reader.readLine()) != null) {
    String[] split = line.split(",");

    Item item = new Item(); // New Item is created for every line
    item.name = split[0];
    item.quantity = Integer.valueOf(split[1]);
    item.price = Double.valueOf(split[2]);
    item.total = item.quantity * item.price;

    items.add(item);
}

I'm creating a list of items from a file

BufferedReader reader = new BufferedReader(
    new InputStreamReader(new FileInputStream("H:/temp/data.csv")));
try {
    List<Item> items = new ArrayList<Item>();
    Item item = new Item();

    String line = null;
    while ((line = reader.readLine()) != null) {
        String[] split = line.split(",");

        item.name = split[0];
        item.quantity = Integer.valueOf(split[1]);
        item.price = Double.valueOf(split[2]);
        item.total = item.quantity * item.price;

        items.add(item);
    }

    for (Item item2 : items) {
        System.out.println("Item: " + item2.name);
    }
} catch (IOException e) {
    reader.close();

    e.printStackTrace();
}

Problem is the list is displaying the last line in the file as the value for all items.

解决方案

The problem with your code is you creating only one instance of Item Object(Item item = new Item) and the same instance is added to the list again and again.

You need to create a new instance of the Item for every line in the file and add it to the list as shown below.

Fix:

List<Item> items = new ArrayList<Item>();

String line = null;
while ((line = reader.readLine()) != null) {
    String[] split = line.split(",");

    Item item = new Item(); // New Item is created for every line
    item.name = split[0];
    item.quantity = Integer.valueOf(split[1]);
    item.price = Double.valueOf(split[2]);
    item.total = item.quantity * item.price;

    items.add(item);
}

这篇关于具有相同值的项目清单的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！