[英]How can sort my hashmap data in ascending order and also descending order
我有一个HashMap<String, List<String>>
myData
我希望能够以升序对我的HashMap
进行排序,然后将其放入一个变量中,该变量将用于迭代并添加到excel文件中。 我还想按降序排序,然后将结果存入一个变量,对其进行迭代,然后将数据添加到excel文件中。 我的HashMap
如下所示: Aug - 19, {"11", "12"} July- 19, {"01", "22"} Jun - 19, {"77", "02"} May - 19, {"99", "42"}
关键是日期。 该值只是一个字符串列表。 我需要检索包含按升序排序的数据的变量,而在另一个变量中按降序排序的数据。 非常感谢您的帮助。
首先将地图中的键转换为更自然的格式,即日期。 然后将它们存储在TreeMap中,TreeMap是一个按顺序存储键的关联容器。
使用parse(String)
获取Date
对象,然后使用format(Date)
重新获得它的字符串形式。
public class DateAsTreeMapKey {
public static void main(String[] args) {
HashMap<String, List<String>> myData = new HashMap<>();
String format = "MMM - yy";
myData.put("Aug - 19", Arrays.asList("11", "12"));
myData.put("July - 19", Arrays.asList("01", "22")); // try out July also
myData.put("Jun - 19", Arrays.asList("77", "02"));
myData.put("May - 19", Arrays.asList("99", "42"));
printDataInAscendingOrder(getDataInSortedForm(myData, format), format);
printDataInDescendingOrder(getDataInSortedForm(myData, format), format);
}
public static TreeMap<Date, List<String>> getDataInSortedForm(HashMap<String, List<String>> myData, String format) {
TreeMap<Date, List<String>> mySortedData = new TreeMap<>();
for (Map.Entry<String, List<String>> entry : myData.entrySet()) {
String monthYear = entry.getKey();
List<String> data = entry.getValue();
try {
Date date = new SimpleDateFormat(format, Locale.ENGLISH).parse(monthYear);
mySortedData.put(date, data);
} catch (ParseException e) {
e.printStackTrace();
}
}
return mySortedData;
}
public static void printDataInAscendingOrder(TreeMap<Date, List<String>> mySortedData, String format) {
System.out.println("Data in ascending order: ");
for (Entry<Date, List<String>> entry : mySortedData.entrySet()) {
System.out.println("Month '" + new SimpleDateFormat(format, Locale.ENGLISH).format(entry.getKey())
+ "' has data as " + entry.getValue().toString());
}
}
public static void printDataInDescendingOrder(TreeMap<Date, List<String>> mySortedData, String format) {
System.out.println("Data in descending order: ");
TreeMap<Date, List<String>> mySortedDataReversed = new TreeMap<>(Collections.reverseOrder());
mySortedDataReversed.putAll(mySortedData);
for (Entry<Date, List<String>> entry : mySortedDataReversed.entrySet()) {
System.out.println("Month '" + new SimpleDateFormat(format, Locale.ENGLISH).format(entry.getKey())
+ "' has data as " + entry.getValue().toString());
}
}
}
打印:
Data in ascending order:
Month 'May - 19' has data as [99, 42]
Month 'Jun - 19' has data as [77, 02]
Month 'Jul - 19' has data as [01, 22]
Month 'Aug - 19' has data as [11, 12]
Data in descending order:
Month 'Aug - 19' has data as [11, 12]
Month 'Jul - 19' has data as [01, 22]
Month 'Jun - 19' has data as [77, 02]
Month 'May - 19' has data as [99, 42]
这是Java 1.8+流版本。 它可能更有效,但是可能会使示例难以理解,因此我将其留给您。 请注意,排序和倒序之间的唯一区别是.reversed()方法。
import org.junit.jupiter.api.Test;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class MapSorter {
@Test
public void test() {
Map<String, List<String>> myData = new HashMap<>();
myData.put("Aug - 19", Arrays.asList("11", "12"));
myData.put("July - 19", Arrays.asList("01", "22")); // try out July also
myData.put("Jun - 19", Arrays.asList("77", "02"));
myData.put("May - 19", Arrays.asList("99", "42"));
myData.keySet().stream()
.map(SortableKey::new)
.sorted(Comparator.comparingLong(SortableKey::getSortableKey))
.map(SortableKey::getOriginalKey)
.forEach(originalKey -> addToExcel(originalKey, myData));
myData.keySet().stream()
.map(SortableKey::new)
.sorted(Comparator.comparingLong(SortableKey::getSortableKey)
.reversed())
.map(SortableKey::getOriginalKey)
.forEach(originalKey -> addToExcel(originalKey, myData));
}
private void addToExcel(String key, Map<String, List<String>> map) {
System.out.println(key + " = " + map.get(key));
}
class SortableKey {
private String dateStr;
private long sortableKey;
SortableKey(String dateStr) {
this.dateStr = dateStr;
try {
sortableKey = new SimpleDateFormat("MMM - yy").parse(dateStr).getTime();
} catch (ParseException e) {
// some type of error handling
}
}
long getSortableKey() {
return sortableKey;
}
String getOriginalKey() {
return dateStr;
}
}
}
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