An enum jiddefinixi tip b'sett fiss ta' kostanti msemmija. L-enums f'Java huma ħafna aktar qawwija minn listi ta' kostanti sempliċi f'lingwi oħra — huma klassijiet kompleti li jistgħu jkollhom fields, konstruttori, u metodi.
{
MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}
Day.MONDAY;
(today) {
MONDAY -> System.out.println();
SATURDAY, SUNDAY -> System.out.println();
-> System.out.println();
}
L-enums jipprovdu type safety — Day today = Day.MONDAY jista' jkun fih biss valuri validi ta' Day, b'differenza minn l-użu ta' ints jew strings arbitrarji bħala kostanti (li jippermettu valuri invalidi u typos).
Day.MONDAY.name(); // "MONDAY"
Day.MONDAY.ordinal(); // 0 — position in the declaration
Day.values(); // array of all constants (iterate them)
Day.valueOf("FRIDAY"); // get a constant by name
for (Day d : Day.values()) { ... } // iterate all values
public enum Planet {
MERCURY(3.3e23, 2.4e6), // each constant calls the constructor with arguments
EARTH(5.97e24, 6.37e6),
JUPITER(1.9e27, 7.1e7);
private final double mass; // enums can have FIELDS
private final double radius;
Planet(double mass, double radius) { // constructor (implicitly private)
this.mass = mass;
this.radius = radius;
}
public double surfaceGravity() { // and METHODS
return 6.67e-11 * mass / (radius * radius);
}
}
Planet.EARTH.surfaceGravity(); // compute using EARTH's data
Kull enum constant hija istanza, konfiggrata permezz tal-konstruttore — u dan jiperrmettilek tassoċja data u imġieba ma' kull constant. Dan huwa uniku u qawwi meta mqabbla ma' l-enums f'ħafna lingwi oħra.
public enum Operation {
PLUS { public int apply(int a, int b) { return a + b; } },
TIMES { public int apply(int a, int b) { return a * b; } };
public abstract int apply(int a, int b); // each constant implements it differently
}
Operation.PLUS.apply(2, 3); // 5
public enum Config { INSTANCE; /* fields/methods */ }
// enum singletons are thread-safe and serialization-safe by design
L-enums f'Java huma mod robustu u type-safe biex tirrappreżenta settijiet fissi ta' kostanti relatati (states, jiem, ruoli, operazzjonijiet) — ħafna aħjar mill-alternattiva error-prone ta' int/String constants, li jippermettu valuri invalidi u ma joffrux type checking.
"/> Ix-xejn uniku qawwi — fields, konstruttori, metodi, interface implementation, u per-constant behavior — jiperrmettilek tgħaqqad data u logika ma' kull constant, modellati concepts ta' domain b'mod elegant (eż. pjaneti b'massa/gravità, operazzjonijiet bl-matematika tagħhom).
Huma wkoll jipprovdu l-isingleton idiom l-aktar sigur.
Fehim tal-enums wara listi sempliċi ta' kostanti — bħala klassijiet kompleti b'state u imġieba — jippermettilek tagħmel domain modeling aktar nadif u sigur, u huwa feature ta' Java mhux ħafna użat imma valwuż ħafna, kif ukoll topik komuni f'intervisti.