Java 如何按升序和降序对hashmap数据进行排序
我有一个Java 如何按升序和降序对hashmap数据进行排序,java,Java,我有一个HashMapmyData我希望能够按升序对我的HashMap进行排序,然后将其放入一个变量中,我将使用该变量迭代并添加到excel文件中。我还想按降序排序,然后在变量中得到结果,迭代它并将数据添加到excel文件中。我的HashMap看起来是这样的:Aug-19,{“11”,“12”}July-19,{“01”,“22”}Jun-19,{“77”,“02”}May-19,{“99”,“42”}关键是日期。这个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,在另一个变量中检索
HashMap
myData
我希望能够按升序对我的HashMap
进行排序,然后将其放入一个变量中,我将使用该变量迭代并添加到excel文件中。我还想按降序排序,然后在变量中得到结果,迭代它并将数据添加到excel文件中。我的HashMap看起来是这样的:Aug-19,{“11”,“12”}July-19,{“01”,“22”}Jun-19,{“77”,“02”}May-19,{“99”,“42”}
关键是日期。这个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,在另一个变量中检索按降序排序的数据。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是一个按排序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)
重新获得该对象的字符串形式
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());
}
}
}
这是一个Java1.8+流版本。它可以更有效,但这可能会混淆示例,所以我将此留给您。请注意,排序和反转顺序之间的唯一区别是.reversed()方法
import org.junit.jupiter.api.Test;
导入java.text.ParseException;
导入java.text.simpleDataFormat;
导入java.util.array;
导入java.util.Comparator;
导入java.util.HashMap;
导入java.util.List;
导入java.util.Map;
公共类地图分拣机{
@试验
公开无效测试(){
Map myData=newhashmap();
myData.put(“8月19日”,Arrays.asList(“11”、“12”);
myData.put(“July-19”,Arrays.asList(“01”,“22”);//也可以试用July
myData.put(“Jun-19”,Arrays.asList(“77”,“02”);
myData.put(“5-19”,Arrays.asList(“99”,“42”);
myData.keySet().stream()
.map(可排序键::新建)
.sorted(Comparator.comparingLong(SortableKey::getSortableKey))
.map(SortableKey::getOriginalKey)
.forEach(originalKey->addToExcel(originalKey,myData));
myData.keySet().stream()
.map(可排序键::新建)
.sorted(Comparator.comparingLong(SortableKey::getSortableKey)
.reversed())
.map(SortableKey::getOriginalKey)
.forEach(originalKey->addToExcel(originalKey,myData));
}
私有void addToExcel(字符串键、映射){
System.out.println(key+“=”+map.get(key));
}
类可排序键{
私有字符串dateStr;
私有长可排序密钥;
SortableKey(字符串dateStr){
this.dateStr=dateStr;
试一试{
sortableKey=newsimpledateformat(“MMM-yy”).parse(dateStr.getTime();
}捕获(解析异常){
//某种类型的错误处理
}
}
长getSortableKey(){
返回可排序键;
}
字符串getOriginalKey(){
返回日期str;
}
}
}
可以使用树形图
而不是哈希图
。您无法对HashMap
进行排序(至少,没有一些严重的黑魔法是不行的)。上面的示例的输出是什么?我想您希望根据“MMM-yy”形式的键进行排序。是这样吗?
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]
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;
}
}
}