如何判断一个枚举值是否存在（Check if an Enum Value Exists in Java）

Searching an Enum by Name

public enum Direction {EAST, WEST, SOUTH, NORTH;public static Direction findByName(String name) {Direction result = null;for (Direction direction : Direction.values()) {if (direction.name().equalsIgnoreCase(name)) {result = direction;break;}}return result;}
}

Direction result1 = Direction .findByName("EAST");
Direction result2 = Direction .findByName("east");
Direction result3 = Direction .findByName("East");
System.out.println(Direction.EAST == result1); // true
System.out.println(Direction.EAST == result2); // true
System.out.println(Direction.EAST == result3); // true

Searching an Enum by Value

public enum Weekday {MONDAY("Monday"), TUESDAY("Tuesday"), SUNDAY("Sunday");private final String value;Weekday(String value) {this.value = value;}public String getValue() {return value;}public static Weekday findByValue(String value) {Weekday result = null;for (Weekday day : Weekday.values()) {if (day.getValue().equalsIgnoreCase(value)) {result = day;break;}}return result;}
}

Weekday result1 = Weekday.findByValue("Monday");
System.out.println(Weekday.MONDAY == result1); // trueWeekday result2 = Weekday.findByValue("mon");
System.out.println(result2); // null

Searching an Enum by Integer Value

public enum Month {JANUARY("January", 1), FEBRUARY("February", 2), // ...DECEMBER("December", 12);private final String value;private final int code;Month(String value, int code) {this.value = value;this.code = code;}public String getValue() {return value;}public int getCode() {return code;}public static Optional<Month> findByCode(int code) {return Arrays.stream(values()).filter(month -> month.getCode() == code).findFirst();}
}

Optional<Month> result = Month.findByCode(1);
System.out.println(Month.JANUARY == result.orElseGet(() -> null)); // trueOptional<Month> result2 = Month.findByCode(0);
System.out.println(result2.orElseGet(() -> null)); // null

Exceptions Thrown from Search Methods

public enum Month {JANUARY("January", 1),FEBRUARY("February", 2),// ...DECEMBER("December", 12);private final String value;private final int code;Month(String value, int code) {this.value = value;this.code = code;}public String getValue() {return value;}public int getCode() {return code;}public static Optional<Month> findByCode(int code) {return Arrays.stream(values()).filter(month -> month.getCode() == code).findFirst();}public static Month findByValue(String value) {return Arrays.stream(values()).filter(month -> month.getValue().equalsIgnoreCase(value)).findFirst().orElseThrow(IllegalArgumentException::new);}
}

Month.findByValue("Jan");Exception in thread "main" java.lang.IllegalArgumentExceptionat java.base/java.util.Optional.orElseThrow(Optional.java:403)at javabasic.enumprac.CheckEnumValueExist$Month.findByValue(CheckEnumValueExist.java:77)at javabasic.enumprac.CheckEnumValueExist.main(CheckEnumValueExist.java:85)

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