Question

我正在做一个学校项目，我需要按花费（降序）打印数组。问题是我通过将5个数组连接成一个并且必须在for循环中收集信息而在其中得到空值，因此我必须在我的代码顶部声明该数组。

所以我的代码是这样的：

                             ⇩

                   Entry | Amount | Category     | Payment | Date

String array[][]={  {"5", "22,2", "car payment", "visa", "21/04/2016"},
                    {"1", "44,4", "shop", "cash", "16/02/2017"},
                    {"2", "33,1", "shop", "cash", "15/01/2020"},
                    {"3", "17,3", "gym", "visa", "10/01/2016"},
                    {null, null, null, null, null},
                    {null, null, null, null, null},
                    {null, null, null, null, null},
                    {null, null, null, null, null},   };

所以我尝试使用Arrays.sort()使用Comparator，但我似乎无法把它弄好，因为我得到了这些空值我总是得到java.lang.NullPointerException。

我试过的是：

Arrays.sort(array, (String[] o1, String[] o2) -> Float.compare(Float.parseFloat(o2[1]), 
                        Float.parseFloat(o1[1])));

我想要的是：

                {"1", "44,4", "shop", "cash", "16/02/2017"},
                {"2", "33,1", "shop", "cash", "15/01/2020"},
                {"5", "22,2", "car payment", "visa", "21/04/2016"},
                {"3", "17,3", "gym", "visa", "10/01/2016"}};

任何帮助都会非常感激。谢谢！

Answer 1

我相信以下代码运作良好：

public class StringArraySorter {
    public static void main(String[] args) {
        String array[][]={  {"5", "22,2", "car payment", "visa", "21/04/2016"},
                {"1", "44,4", "shop", "cash", "16/02/2017"},
                {"2", "33,1", "shop", "cash", "15/01/2020"},
                {"3", "17,3", "gym", "visa", "10/01/2016"},
                {null, null, null, null, null},
                {null, null, null, null, null},
                {null, null, null, null, null},
                {null, null, null, null, null},
        };

        Arrays.sort(array, new Comparator<String[]>() {
            @Override
            public int compare(String[] o1, String[] o2) {
                String a1 = o1[1]; // amount field
                String a2 = o2[1]; // amount field
                if (a1 != null && a2 != null) {
                    a1 = a1.replace(',', '.');
                    a2 = a2.replace(',', '.');
                    return Float.compare(Float.parseFloat(a2), Float.parseFloat(a1));
                }
                return 1; // non-null value for amount takes precedence, whatever that may be
            }
        });
        System.out.println(Arrays.deepToString(array));
    }
}

它打印（修改为插入换行符），符合您的要求：

[[1, 44,4, shop, cash, 16/02/2017], 
[2, 33,1, shop, cash, 15/01/2020], 
[5, 22,2, car payment, visa, 21/04/2016], 
[3, 17,3, gym, visa, 10/01/2016], 
[null, null, null, null, null], 
[null, null, null, null, null], 
[null, null, null, null, null], 
[null, null, null, null, null]]

现在，您可以始终修剪您的输入数组，以便在发送数组之前删除具有某些关键字段null（或以其他方式无效）的记录（字符串数组）到Arrays.sort方法。使用Java 8构造（但可以说有点神秘）的初步尝试是：

Arrays.stream(array).filter(a -> a[2] != null)
            .sorted((o1, o2) -> Float.compare(Float.parseFloat(o1[1].replace(',', '.')), Float.parseFloat(o1[1].replace(',', '.'))))
            .forEach(a -> System.out.println("{" + Arrays.stream(a).map(s -> "\"" + s + "\"").collect(Collectors.joining(", ")) +
            "}"));

打印：

{"1", "44,4", "shop", "cash", "16/02/2017"}
{"2", "33,1", "shop", "cash", "15/01/2020"}
{"5", "22,2", "car payment", "visa", "21/04/2016"}
{"3", "17,3", "gym", "visa", "10/01/2016"}

按列打印2d String数组

1 个答案: