遍历列表列表并使用 java 8 检查条件

Question

我正在尝试遍历元素列表以测试给定条件，而使用 Java 7 是可能的，我很想知道如何使用 java 8 流.

import java.util.Arrays;
import java.util.List;
import java.util.Objects;

public class Main2 {
    static String[] positionsThatWillBeCovered = new String[]{"RB", "LB", "MD"};
    static String[] positionsThatWillNotBeCovered = new String[]{"RB", "LB", "MD", "GK"};

    public static void main(String[] args) {
        Position p1 = new Position("RB");
        Position p2 = new Position("LB");
        Position p3 = new Position("MD");

        Player alves = new Player(Arrays.asList(p1, p2));
        Player alba = new Player(Arrays.asList(p2));
        Player xavi = new Player(Arrays.asList(p3));

        Team team = new Team(Arrays.asList(alves, alba, xavi));

        //should print true
        System.out.println(testAllPositionsAreCovered(team, positionsThatWillBeCovered));

        //false
        System.out.println(testAllPositionsAreCovered(team, positionsThatWillNotBeCovered));
    }

    private static boolean testAllPositionsAreCovered(Team team, String[] positionsToCover) {
        for (String positionToCover : positionsToCover) { 
            boolean positionWasCovered = false;
            A : for (Player player : team.getPlayerList()) {
                   for (Position playerPosition : player.getPositions()) {
                        if(playerPosition.getPosition().equals(positionToCover))
                        {
                            positionWasCovered = true;
                            break A;
                        }
                    }
                }
                if (!positionWasCovered) return false;
            }
        return true;
    }
}

class Team {
    private List<Player> playerList;
    Team(List<Player> playerList){
        this.playerList = playerList;
    }

    public List<Player> getPlayerList() {
        return playerList;
    }
}

class Player {
    private List<Position> positions;
    Player(List<Position> positions){
        this.positions = positions;
    }

    public List<Position> getPositions() {
        return positions;
    }
}

class Position {
    private String position;
    //some other fields...
    public Position(String position) {
        this.position = position;
    }

    public String getPosition() {
        return position;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Position position1 = (Position) o;
        return Objects.equals(position, position1.position);
    }

    @Override
    public int hashCode() {
        return Objects.hash(position);
    }
}

一个Team包含一个Players列表，一个Player可以打多个位置

问题： 给定一支球队和一份位置列表，我需要知道是否列表中的每个位置都至少可以由一名球员担任。

我有一个 Java 7 的解决方案，我们可以遍历所有位置并检查是否至少有一个玩家可以玩。

我对 java 8 流解决方案感兴趣。

谢谢。

编辑：顺便说一下，在@Holger 的评论之后，我更新了我的 java 7 版本的解决方案，它是一种更好的方式。

这是我更改的部分：

private static boolean testAllPositionsAreCovered(Team team, String[] positionsToCover) {
    for (String positionToCover : positionsToCover) { //"RB", "LB", "MD"
        if (!isThePositionCoveredByAPlayer(team, positionToCover))
            return false;
    }
    return true;
}

private static boolean isThePositionCoveredByAPlayer(Team team, String positionToCover) {
    for (Player player : team.getPlayerList()) {
         for (Position playerPosition : player.getPositions()) {
              if(playerPosition.getPosition().equals(positionToCover))
                return true;
         }
    }
    return false;
}

Answer 1

使用flatMap将所有玩家的位置合并为一个流：

public boolean testAllPositionsAreCovered(Team team,
                                          String[] positions) {

    Set<String> positionsOfTeams = team.getPlayers().stream()
        .flatMap(p -> p.getPositions().stream())
        .map(Position::getPosition)
        .collect(Collectors.toSet());
    return positionsOfTeams.containsAll(Arrays.asList(positions));
}

遍历列表列表并使用 java 8 检查条件

Iterate over a list of lists and check for a condition using java 8

java

java-8

stream

flatmap