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

超、凢脫俗 2024-03-23 17:24 120阅读 0赞

#### 目录 ####

*   *  Searching an Enum by Name
     *  Searching an Enum by Value
     *  Searching an Enum by Integer Value
     *  Exceptions Thrown from Search Methods

### 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); // true
    
    Weekday 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)); // true
    
    Optional<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.IllegalArgumentException
    	at 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)

\-----------------------------------------------------------------------------读书笔记摘自 文章：[Check if an Enum Value Exists in Java][]

[Check if an Enum Value Exists in Java]: https://www.baeldung.com/java-search-enum-values