[英]Filter an Optional<List<Object>> in java8
我正在嘗試在Java8中過濾Optional<List<Object>>
。 在下面的示例中,我嘗試過濾列表,而不收集完整列表(玩家)。 這可能嗎?
public List<Player> getPlayers(int age, Team team) {
Optional.ofNullable(team).map(Team::getPlayers);
// needs to filter players older than 20 years, without collecting it as a list.
}
class Team {
String name;
List<Player> players;
public String getName() {
return name;
}
public void setName(final String name) {
this.name = name;
}
public List<Player> getPlayers() {
return players;
}
public void setPlayers(final List<Player> players) {
this.players = players;
}
}
class Player {
String playerName;
String age;
public String getPlayerName() {
return playerName;
}
public void setPlayerName(final String playerName) {
this.playerName = playerName;
}
public String getAge() {
return age;
}
public void setAge(final String age) {
this.age = age;
}
}
使用該方法的更新簽名,您似乎正在尋找的是:
public List<Player> getPlayers(Team team, int age) {
return Optional.ofNullable(team).map(Team::getPlayers)
.orElse(Collections.emptyList())
.stream()
.filter(a -> Integer.parseInt(a.getAge()) > 20)
.collect(Collectors.toList());
}
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