Question

我有一个具有一种属性类型的对象的列表。我想过滤该列表以仅包含其值在Enum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());
    }
}

我只想保留玩家列表中属于枚举列表的那些项目。以上似乎不起作用。请提出一种实现此目标的方法。我正在Java 8中执行此操作。

Answer 1

您的枚举甚至没有编译。一旦有了一个可以正常使用的最小的完整示例，您只需使用arr[arr[0]-1] = -arr[arr[0]-1]; arr[0]=-1; if i = 1, arr[1] =-2; if i = 2 , arr[2]=-3; if i = 3 , arr[arr[3]-1] which will be arr[2] which is already negative, so this the duplicate element。

Collections.removeIf

更新：原始张贴者说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); } }的商店类型为Player（无论出于何种原因）。因此需要根据枚举类型进行查找（或仅使用String）。

Set<String> playerTypes

Answer 2

根据我的说法，有两种方法：

*使用枚举名称代替创建带有枚举的玩家类型列表：

[1, 3 ,5, 7, NaN, NaN, NaN, 15, NaN]

*您可以使用enum类的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()); } }方法将从valueOf获得的字符串转换为Enum：

p.getType()

Answer 3

如果要查找枚举是否具有字符串，我将向该枚举添加一个Hashmap并将其值添加为键。这样，我可以做一个简单的获取并检查它是否存在。

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我们的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());
}

我已经尝试过此代码，并且可以按预期工作。请告诉我是否有帮助。

检查枚举列表是否包含Java中的字符串

3 个答案: