public static Map parseListToMap(Collection list, Function mapper) {
if (list == null || list.size() == 0) {
return null;
}
Map map = new HashMap<>();
for (V v : list) {
map.put(mapper.apply(v), v);
}
return map;
}
public static Map> parseListToListMap(List list, Function mapper) {
if (list == null || list.size() == 0) {
return null;
}
Map> map = new HashMap<>();
for (V v : list) {
if (map.containsKey(mapper.apply(v))) {
map.get(mapper.apply(v)).add(v);
}
else {
List values = new ArrayList<>();
values.add(v);
map.put(mapper.apply(v), values);
}
}
return map;
}
public static Map frequencyOfListElements(Collection list, Function mapper) {
if (null == list || list.size() == 0) {
return null;
}
Map map = new HashMap<>();
for (V v : list) {
Integer count = map.get(mapper.apply(v));
map.put(mapper.apply(v), (null == count) ? 1 : (count + 1));
}
return map;
}
Original: https://www.cnblogs.com/eternality/p/16699600.html
Author: 逆梦
Title: java处理集合工具
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