3 回答

TA贡献1839条经验 获得超15个赞
您可以将 Comparator 作为参数传递给 Map 的构造函数。根据文档,它仅用于键:
/**
* 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;
}
通过这种方式,您可以通过密钥长度传递比较器,如下所示:
new TreeMap<>(Comparator.comparingInt(String::length).thenComparing(Comparator.naturalOrder()))

TA贡献1891条经验 获得超3个赞
您需要为此编写自己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);
}
}
这不处理null值,但如果您null在用例中期望值,您可以添加处理。

TA贡献1777条经验 获得超10个赞
您可以按如下方式执行此操作。
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 的定义如下。
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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