我仍然是Java 8的初学者。我一直在过滤List of List值。这是我的代码
5如何更正public class MapFilterList {
private static Map<String, List<Person>> personMap = new HashMap<>();
public static void main(String[] args) {
Person p1 = new Person("John", 22);
Person p2 = new Person("Smith", 45);
Person p3 = new Person("Sarah", 27);
List<Person> group1 = new ArrayList<>();
group1.add(p1);
group1.add(p2);
List<Person> group2 = new ArrayList<>();
group2.add(p2);
group2.add(p3);
List<Person> group3 = new ArrayList<>();
group3.add(p3);
group3.add(p1);
personMap.put("group1", group1);
personMap.put("group2", group2);
personMap.put("group3", group3);
doFilter("group1").forEach(person -> {
System.out.println(person.getName() + " -- " + person.getAge());
});
}
public static List<Person> doFilter(String groupName) {
return personMap.entrySet().stream().filter(key -> key.equals(groupName)).map(map -> map.getValue()).collect(Collectors.toList());
}
}
方法，因为错误显示doFilter。
答案 0 :(得分：8)
如果我理解正确，您需要以下代码：
public static List<Person> doFilter(String groupName) {
return personMap.entrySet().stream()
.filter(entry -> entry.getKey().equals(groupName))
.map(entry -> entry.getValue())
.flatMap(List::stream)
// as an option to replace the previous two
// .flatMap(entry -> entry.getValue().stream())
.collect(Collectors.toList());
}