按列打印2d字符串數組

Question

我正在做一個學校項目，我需要按花費的數量（降序）打印數組。問題是，我通過將5個數組合併成一個，並且必須在for循環中收集信息來獲得空值，所以我必須在我的代碼頂部聲明數組。

所以我的代碼是這樣的：

       ⇩ 

        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}, }; 

所以我試圖用Arrays.sort()使用Comparator，但我似乎無法得到它的權利，因爲我得到了那些空裏面我總是java.lang.NullPointerException。

我想這是什麼：

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

什麼我想要得到的是：

   {"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"}}; 

任何幫助，將如此讚賞。謝謝！

Answer 1

我相信下面的代碼工作得相當好：

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，插入新行），這是接近你的要求：

[[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]] 

現在，你總是可以修剪您的輸入數組將在將數組發送到Arrays.sort方法之前刪除具有某些關鍵字段null（或以某種其他方式無效）的記錄（字符串數組）。它使用Java 8構造（但可以說，有點神祕）將是一個初步嘗試：

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"}