我正在尝试对 java.util.Map
进行如下排序。
public final class SortMapByValue <K, V extends Comparable<? super V>> implements Comparator<Map.Entry<K, V>>
{
@Override
public int compare(Entry<K, V> o1, Entry<K, V> o2) {
return (o1.getValue()).compareTo(o2.getValue());
}
public static <K, V extends Comparable<? super V>> Map<K, V> sortMapByValue(Map<K, V> unsortedMap)
{
List<Map.Entry<K, V>> list = new LinkedList<Map.Entry<K, V>>(unsortedMap.entrySet());
Collections.sort(list); //Compiler error here.
Map<K, V> sortedMap = new LinkedHashMap<K, V>();
for (Map.Entry<K, V> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
return sortedMap;
}
}
如代码中所注释的那样,它会发出以下编译时错误。
no suitable method found for sort(List<Entry<K,V>>)
method Collections.<T#1>sort(List<T#1>,Comparator<? super T#1>) is not applicable
(cannot instantiate from arguments because actual and formal argument lists differ in length)
method Collections.<T#2>sort(List<T#2>) is not applicable
(inferred type does not conform to declared bound(s)
inferred: Entry<K,V>
bound(s): Comparable<? super Entry<K,V>>)
where K,V,T#1,T#2 are type-variables:
K extends Object declared in method <K,V>sortMapByValue(Map<K,V>)
V extends Comparable<? super V> declared in method <K,V>sortMapByValue(Map<K,V>)
T#1 extends Object declared in method <T#1>sort(List<T#1>,Comparator<? super T#1>)
T#2 extends Comparable<? super T#2> declared in method <T#2>sort(List<T#2>)
以下是在 sortMapByValue()
方法中以以下方式完成的。
Collections.sort(list, new Comparator<Map.Entry<K, V>>()
{
@Override
public int compare(Map.Entry<K, V> o1, Map.Entry<K, V> o2) {
return (o1.getValue()).compareTo(o2.getValue());
}
});
相反,我想修复该错误并遵循这种方式(避免使用匿名比较器)。如何解决此错误?
Entry
列表。类Entry
没有实现Comparable
接口。然而,Collections.sort(..)
期望一个实现了Comparable
接口的类型的列表。 - Sotirios Delimanolis