检查枚举列表是否包含Java中的字符串

Question

我有一个具有一种属性类型的对象列表。我想过滤该列表以仅包含其值在枚举列表中的那些对象。

这是上面描述的 Java 程序的简单版本。

public enum Types {SLOW("Slow"), FAST("Fast"), VERY_FAST("Running");}
List<Types> playerTypes = new ArrayList<>();
playerTypes.add(Types.SLOW);
List<Player> myPlayers = new ArrayList<>();
Player player = new Player("FAST");
myPlayers.add(player);
for (Player p : myPlayers) {
    if(playerTypes.contains(p.getType())) {
       System.out.println("Player type is : " + p.getType());
    }
}

我只想保留那些属于枚举列表一部分的播放器列表中的项目。以上似乎不起作用。请提出一种方法来实现这一点。我在 Java 8 中这样做。

Answer 1

据我所知，有两种方法：

*不要使用枚举创建玩家类型列表，而是使用枚举名称：

public enum Types {
    SLOW("Slow"), FAST("Fast"), VERY_FAST("Running");
}
List<String> playerTypes = new ArrayList<>();
playerTypes.add(Types.SLOW.name());
List<Player> myPlayers = new ArrayList<>();
Player player = new Player("FAST");
myPlayers.add(player);
for (Player p : myPlayers) {
    if(playerTypes.contains(p.getType())) {
       System.out.println("Player type is : " + p.getType());
    }
}

*可以使用枚举类的valueOf方法，将从p.getType()获取的字符串转换为Enum：

public enum Types {
    SLOW("Slow"), FAST("Fast"), VERY_FAST("Running");
}
List<Types> playerTypes = new ArrayList<>();
playerTypes.add(Types.SLOW);
List<Player> myPlayers = new ArrayList<>();
Player player = new Player("FAST");
myPlayers.add(player);
for (Player p : myPlayers) {
    if(playerTypes.contains(Types.valueOf(p.getType()))) {
       System.out.println("Player type is : " + p.getType());
    }
}

Answer 2

你的枚举甚至没有编译。一旦你得到了一个可以正常工作的最小完整示例，你只需要使用Collections.removeIf。

import java.util.*;
import java.util.stream.*;

enum PlayerType {
    SLOW, FAST, VERY_FAST
}
class Player {
    private final PlayerType type;
    public Player(PlayerType type) {
        this.type = type;
    }
    public PlayerType type() {
        return type;
    }
    @Override public String toString() {
        return type.name();
    }
}
interface Play {
   static void main(String[] args) {
       Set<PlayerType> playerTypes = EnumSet.of(
           PlayerType.SLOW
       );
       List<Player> myPlayers = new ArrayList<>(Arrays.asList(
          new Player(PlayerType.FAST)
       ));
       myPlayers.removeIf(player -> !playerTypes.contains(player.type()));
       System.err.println(myPlayers);
   }
}

更新： 原始发帖者说Player 商店输入String（无论出于何种原因）。所以这需要查找枚举类型（或者只使用Set<String> playerTypes）。

   myPlayers.removeIf(player -> 
       !playerTypes.contains(PlayerType.valueOf(player.type()))
   );

Answer 3

如果你想查找一个 Enum 是否有一个字符串，我会在我们的 Enum 中添加一个 Hashmap 并将我们的值作为键添加。这样，我可以做一个简单的 get 并检查它是否存在。

public enum PlayerSpeed {

    // Type of speeds.
    SLOW("Slow"),
    FAST("Fast"),
    VERY_FAST("Running");

    // String value that represents each type of speed.
    public final String value;
    // Hash map that let us get a speed type by it's String value.
    private static Map map = new HashMap<>();

    // Private constructor.
    private PlayerSpeed(String value) { this.value = value; }

    // Fill our hash map.
    static {
        for (PlayerSpeed playerSpeed : PlayerSpeed.values()) {
            map.put(playerSpeed.value, playerSpeed);
        }
    }

    /**
     * Given a string, look it up in our enum map and check if it exists.
     * @param searchedString String that we are looking for.
     * @return True if the string is found.
     */
    public static boolean containsString(String searchedString) {
        return map.get(searchedString) != null;
    }

}

然后，您需要做的就是使用 Enum 的 containsString 方法检查字符串是否存在。

Player player = new Player("FAST");
if(PlayerSpeed.constainsString(p.getType())) {
   System.out.println("Player type is : " + p.getType());
}

我已经尝试过这段代码，它按预期工作。如果有帮助，请告诉我。