按當前月份排序List<Object>到最近六個月

我的串列中有以下資料：

    List<FeatureAnalyzeDTOResult> list = new ArrayList<>();
    list.add(new FeatureAnalyzeDTOResult("october", 46));
    list.add(new FeatureAnalyzeDTOResult("april", 46));
    list.add(new FeatureAnalyzeDTOResult("march", 46));
    list.add(new FeatureAnalyzeDTOResult("november", 30));
    list.add(new FeatureAnalyzeDTOResult("may", 46));
    list.add(new FeatureAnalyzeDTOResult("january", 53));
    list.add(new FeatureAnalyzeDTOResult("december", 30));

我想做什么？
我正在嘗試按順序對這些資料進行排序，以便資料按月份排序，月份應從當前月份開始并計算前六個月。
例如：
目前是五月，資料應按以下順序排序：

[MAY, APRIL, MARCH, FEBRUARY, JANUARY, DECEMBER]    

如果缺少任何月份，它應該簡單地跳過它并繼續下個月并完成計數。

到目前為止我嘗試了什么？

我嘗試了以下代碼來獲取當前月份和前六個月：

        YearMonth thisMonth = YearMonth.now();
    String[] month = new String[6];
    for (int i = 0; i < 6; i  ) {
        YearMonth lastMonth = thisMonth.minusMonths(i);
        DateTimeFormatter monthYearFormatter = DateTimeFormatter.ofPattern("MMMM");
        month[i] = lastMonth.format(monthYearFormatter);
        month[i] = month[i].toUpperCase();
    }

    List<String> monthList = Arrays.asList(month);
    System.out.println(monthList);

我也試過寫一個Comparator，但它沒有按預期作業。我對撰寫Comparator.

        Comparator<FeatureAnalyzeDTOResult> comp = (o1, o2)
            -> monthList.indexOf(o2.getMonth().toUpperCase()) - monthList.indexOf(o1.getMonth().toUpperCase());
    list.sort(comp);

它給出的輸出如下：

     [Feature: december Count: 30 
         , Feature: january Count: 53 
         , Feature: march Count: 46 
         , Feature: april Count: 46 
         , Feature: may Count: 46 
         , Feature: october Count: 46 
         , Feature: november Count: 30]

這是FeatureAnalyzeDTOResult供參考的課程：

class FeatureAnalyzeDTOResult {

private String month;
private int count;

public FeatureAnalyzeDTOResult(String feature, int count) {
    this.month = feature;
    this.count = count;
}

  public FeatureAnalyzeDTOResult() {
}
public String getMonth() {
    return month;
}

public void setMonth(String feature) {
    this.month = feature;
}

public int getCount() {
    return count;
}

public void setCount(int count) {
    this.count = count;
}

@Override
public String toString() {
    StringBuilder string = new StringBuilder();
    string.append("Feature: ").append(getMonth()).append(" Count: ").append(getCount()).append(" \n");
    return string.toString();
}

uj5u.com熱心網友回復：

這里有一種替代方法：

• 從API的Month列舉中獲取月份串列java.time
• Collections.rotate使用當前月份值旋轉串列
• 使用反轉串列Collections.reverse
• 根據上面串列的索引創建一個比較器來比較月份
• 流式傳輸、排序和限制

就像是

import java.util.Collections;
import java.util.Comparator;

public static void main(String[] args) {
    List<FeatureAnalyzeDTOResult> list = new ArrayList<>();
    list.add(new FeatureAnalyzeDTOResult("october", 46));
    list.add(new FeatureAnalyzeDTOResult("april", 46));
    list.add(new FeatureAnalyzeDTOResult("march", 46));
    list.add(new FeatureAnalyzeDTOResult("november", 30));
    list.add(new FeatureAnalyzeDTOResult("may", 46));
    list.add(new FeatureAnalyzeDTOResult("january", 53));
    list.add(new FeatureAnalyzeDTOResult("december", 30));


    List<Month> months = new ArrayList<>(Arrays.asList(Month.values()));
    Collections.rotate(months, 12 - YearMonth.now().getMonthValue());
    Collections.reverse(months);

    Comparator<FeatureAnalyzeDTOResult> comp =
            Comparator.comparingInt(f -> months.indexOf(Month.valueOf(f.getMonth().toUpperCase())));

    list.stream().sorted(comp).limit(6).forEach(System.out::println);
}

uj5u.com熱心網友回復：

假設當前月份將獲得整數 0（或 11），然后為每個月分配一個連續的 int。

例如，五月 = 0，六月 = 1，.... 一月 = 8...

然后，對您的輸入陣列進行排序，然后從那里開始，問題真的很簡單

uj5u.com熱心網友回復：

這是我的做法：

enum Month {
    JANUARY,
    FEBRUARY,
    MARCH,
    APRIL,
    MAY,
    JUNE,
    JULY,
    AUGUST,
    SEPTEMBER,
    OCTOBER,
    NOVEMBER,
    DECEMBER
}
public static void main(String[] args) {
    List<String> data = Arrays.asList("october", "april", "march", "november", "may", "january", "december");
    Month currentMonth = Month.MAY;
    List<String> thisYear = data.stream()
                                .filter(a -> Month.valueOf(a.toUpperCase()).ordinal() <= currentMonth.ordinal())
                                .collect(Collectors.toList());
    List<String> lastYear = data.stream()
                                .filter(a -> Month.valueOf(a.toUpperCase()).ordinal() > currentMonth.ordinal())
                                .collect(Collectors.toList());
    Comparator<String> monthComparator = new Comparator<String>() {

        @Override
        public int compare(String a, String b) {    
            Month mA = Month.valueOf(a.toUpperCase());
            Month mB = Month.valueOf(b.toUpperCase());
            return mB.compareTo(mA);
        }
    };
    thisYear.sort(monthComparator);
    lastYear.sort(monthComparator);
    
    thisYear.addAll(lastYear);
    System.out.println(thisYear);
}

uj5u.com熱心網友回復：

你快到了。你缺少的是兩件事：

1. 您忘記過濾掉超過 6 個月前的月份。
2. 你得到了相反的比較（所以你看到的是升序而不是降序）。

以下同時進行過濾和排序：

    Comparator<FeatureAnalyzeDTOResult> comp =
            Comparator.comparingInt(o -> monthList.indexOf(o.getMonth().toUpperCase()));
    list = list.stream()
            .filter(o -> monthList.contains(o.getMonth().toUpperCase()))
            .sorted(comp)
            .toList();
    System.out.println(list);

輸出：

[Feature: may Count: 46 
, Feature: april Count: 46 
, Feature: march Count: 46 
, Feature: january Count: 53 
, Feature: december Count: 30 
]

標籤：爪哇 排序 数组列表

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