我想將鍵值對存儲在 TreeMap 中，并根據以下邏輯根據 Key 的值對條目進行排序：按密鑰長度排序。如果兩個鍵的長度相同，則按字母順序對其進行排序。例如，對于以下鍵值對。IBARAKI MitoCityTOCHIGI UtunomiyaCityGUNMA MaehashiCitySAITAMA SaitamaCityCHIBA ChibaCityTOKYO SinjyukuKANAGAWA YokohamaCity預期的輸出是這樣的。CHIBA : ChibaCityGUNMA : MaehashiCityTOKYO : SinjyukuIBARAKI : MitoCitySAITAMA : SaitamaCityTOCHIGI : UtunomiyaCityKANAGAWA : YokohamaCity
3 回答
紫衣仙女
TA貢獻1839條經驗 獲得超15個贊
您可以將 Comparator 作為參數傳遞給 Map 的構造函數。根據文檔，它僅用于鍵：
/**
* Constructs a new, empty tree map, ordered according to the given
* comparator. All keys inserted into the map must be <em>mutually
* comparable</em> by the given comparator: {@code comparator.compare(k1,
* k2)} must not throw a {@code ClassCastException} for any keys
* {@code k1} and {@code k2} in the map. If the user attempts to put
* a key into the map that violates this constraint, the {@code put(Object
* key, Object value)} call will throw a
* {@code ClassCastException}.
*
* @param comparator the comparator that will be used to order this map.
* If {@code null}, the {@linkplain Comparable natural
* ordering} of the keys will be used.
*/
public TreeMap(Comparator<? super K> comparator) {
this.comparator = comparator;
}
通過這種方式，您可以通過密鑰長度傳遞比較器，如下所示：
new TreeMap<>(Comparator.comparingInt(String::length).thenComparing(Comparator.naturalOrder()))
萬千封印
TA貢獻1891條經驗 獲得超3個贊
您需要為此編寫自己comparator的并在 中使用它TreeMap，例如：
public class StringComparator implements Comparator<String> {
@Override
public int compare(String s1, String s2) {
return s1.length() == s2.length() ? s1.compareTo(s2) : s1.length() - s2.length();
}
public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
Map<String, String> map = new TreeMap<>(new StringComparator());
map.put("IBARAKI", "MitoCity");
map.put("TOCHIGI", "UtunomiyaCity");
map.put("GUNMA", "MaehashiCity");
map.put("SAITAMA", "SaitamaCity");
map.put("CHIBA", "ChibaCity");
map.put("TOKYO", "Sinjyuku");
map.put("KANAGAWA", "YokohamaCity");
System.out.println(map);
}
}
這不處理null值，但如果您null在用例中期望值，您可以添加處理。
不負相思意
TA貢獻1777條經驗 獲得超10個贊
您可以按如下方式執行此操作。
public static void main(String[] args) {
Map<String, String> map = new TreeMap<>(new CustomSortComparator());
map.put("IBARAKI", "MitoCity");
map.put("TOCHIGI", "UtunomiyaCity");
map.put("GUNMA", "MaehashiCity");
map.put("SAITAMA", "SaitamaCity");
map.put("CHIBA", "ChibaCity");
map.put("TOKYO", "Sinjyuku");
map.put("KANAGAWA", "YokohamaCity");
System.out.println(map);
}
CustomSortComparator 的定義如下。
public class CustomSortComparator implements Comparator<String> {
@Override
public int compare(String o1, String o2) {
if (o1.length() > o2.length()) {
return 1;
}
if (o1.length() < o2.length()) {
return -1;
}
return returnCompareBytes(o1, o2);
}
private int returnCompareBytes(String key1, String key2) {
for (int i = 0; i < key1.length() - 1; i++) {
if (key1.charAt(i) > key2.charAt(i)) {
return 1;
}
if (key1.charAt(i) < key2.charAt(i)) {
return -1;
}
}
return 0;
}
}
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