X'inhuma l-objekti immutabbli u għal-liex jintużaw?

Question

Accepted Answer

Objett **immutabbli** ma jistax jinbidel wara li jinħoloq — kull field huwa ssettjat darba, u m'hemm l-ebda metodi li jibdlu l-istat. Biex "tibiddel" it-oġġett, inti toħloq oġġett ġdid.

## Bini tip immutabbli

```java
public final class Money {              // final: can't be subclassed to add mutation
    private final int cents;            // final fields, set once
    private final String currency;

public Money(int cents, String currency) {
        this.cents = cents;
        this.currency = currency;
    }

public Money plus(Money other) {    // returns a NEW object, no mutation
        return new Money(this.cents + other.cents, currency);
    }
    public int cents() { return cents; }
}
```

`plus` ma jibdilx `this`; jirritorna `Money` ġdid.

## Għal-liex l-immutabbiltà tgħin

```text
✓ Thread-safe by default → no shared mutable state, no locks needed
✓ Safe to share/cache    → no defensive copies
✓ Valid forever          → if valid at construction, stays valid
✓ Usable as map keys     → hashCode never changes
```

## Trade-off

```text
⚠️ Creates new objects on every change → more allocation/GC pressure
⚠️ Awkward for large objects updated frequently (mitigated by builders / persistent
   data structures)
```

Offgħal mill-immutabbiltà *bajda*: field `final` li jwissi għal lista mutabbli għadu mutabbli permezz ta' dik ir-referenza. Kopja b'mod defensiv jew uża kollezzjonijiet li ma jistgħux jinbidlu.

## Għal-liex dan importanti

L-immutabbiltà telimina klassi sħiħa ta' bugs: xejn ma jistax ibiddel oġġett mingħajr ma tkunx taf, u għalhekk ir-raġunament u l-konkorrenza ssiru drammatiċċament aktar sempliċi.

Dan huwa għal-liex it-tipi ta' valur (strings, `LocalDate`, records) huma immutabbli fil-lingwi moderni — kondiviżi, cachati, u użati b'mod sigur bħala ċavit mingħajr kopja defensiva.