SatyaCodes

Java- Enums

Enums

An enum is a special “class” that represents a group of constants (unchangeable variables, like final variables).

An enum can, just like a class, have attributes and methods. The only difference is that enum constants are public, static and final (unchangeable - cannot be overridden).

An enum cannot be used to create objects, and it cannot extend other classes (but it can implement interfaces).

To create an enum, use the enum keyword (instead of class or interface), and separate the constants with a comma. Note that they should be in uppercase letters:

enum Level {
  LOW,
  MEDIUM,
  HIGH
}

You can access enum constants with the . syntax: Level myVar = Level.MEDIUM;

Enum with Values & Methods

  1. Identify the required aruments
  2. Create Enums by passing aruments values
  3. Write methods for getting values getDepartmentByCode & getDepartmentValues
  4. You can also group enums by EnumSet, we also have EnumMap
  5. You can define methods with default implemetations, which is common for all enums.
  6. You can override default method implenetation for specific eums.
@AllArgsConstructor
public enum DepartmentEnum {

    //Define Values for Enum with arguments
    IT("IT", "IT Engineering", "ENGINEERING"),
    CSE("CSE", "Computer Science Engineering", "ENGINEERING"),
    ECE("ECE", "Electronics Engineering", "ENGINEERING"),



    MBBS("MBBS", "Bachelor in Medicine", "MEDICINE"){
        @Override
        public void print() {
            System.out.println("MBBS : Override Print : "+this.getLabel());
        }
    },

    MD("MD", "Masters in Medicine", "MEDICINE"){
        @Override
        public void print() {
            System.out.println("MD : Override Print : "+this.getLabel());
        }
    };


    private static EnumSet<DepartmentEnum> engineeringSet =
            EnumSet.of(DepartmentEnum.CSE, DepartmentEnum.IT, DepartmentEnum.ECE);

    private static EnumSet<DepartmentEnum> medicineSet =
            EnumSet.of(DepartmentEnum.MBBS, DepartmentEnum.MD);


    //Define arguments for Enum
    @Getter
    private final String code;
    @Getter
    private final String label;
    @Getter
    private final String field;

    public static DepartmentEnum getDepartmentByCode(String code) {
        return DepartmentEnum.valueOf(code);
    }

    public static List<DepartmentEnum> getDepartmentValues() {
        return Stream.of(DepartmentEnum.values()).collect(Collectors.toList());
    }

    public void print() {
        System.out.println("Default Print");
    }
}

Test this code

public static void enumChecking(){

    log.info("Printing Enums");
    log.info("CSE : "+DepartmentEnum.CSE.getCode()+", Value: "+DepartmentEnum.CSE.getLabel());
    log.info("ECE : "+DepartmentEnum.ECE.getCode()+", Value: "+DepartmentEnum.ECE.getLabel());
    log.info("Value by code MBBS: "+DepartmentEnum.getDepartmentByCode("MBBS"));

    DepartmentEnum.CSE.print();
    DepartmentEnum.MBBS.print();
}

Output

Printing Enums
CSE : CSE, Value: Computer Science Engineering
ECE : ECE, Value: Electronics Engineering
Value by code MBBS: MBBS
Default Print
MBBS : Override Print : Bachelor in Medicine

I know this is very Basic. But we can use Enums for Implement Design Patterns. Will update this post with Design pattern implementation.

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