目录
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