Apa iku coupling lan cohesion?

Question

Accepted Answer

**Coupling** ngukur sakmene siji modul gumantung ing modul liyane; **cohesion** ngukur sakmene kuat bagian *ing jero* modul kuwi cocog banget. Tujuane: **coupling kurang, cohesion dhuwur**.

## Kaloro sumbu

```text
HIGH cohesion  → a class does ONE well-defined job, parts relate strongly  ✅
LOW  coupling  → modules interact through small, stable interfaces         ✅
```

## Cohesion kurang (ala) vs. cohesion dhuwur (apik)

```python
# LOW cohesion: unrelated responsibilities jammed together
class Utils:
    def parse_csv(self, s): ...
    def send_email(self, to): ...
    def hash_password(self, p): ...   # nothing in common

# HIGH cohesion: each class has a single, focused purpose
class CsvParser:     ...
class Mailer:        ...
class PasswordHasher: ...
```

## Coupling ketat vs. coupling kendor

```python
# TIGHT: OrderService is welded to a concrete class
class OrderService:
    def __init__(self):
        self.db = MySqlDatabase()        # can't swap or test in isolation

# LOOSE: depends on an abstraction, injected in
class OrderService:
    def __init__(self, db: Database):    # any Database works
        self.db = db
```

Coupling kendor ngidini kowe ngganti `MySqlDatabase` karo fake in-memory kanggo tes, tanpa owah `OrderService`.

## Mulane penting

Coupling ketat kuwi sing nggawe owah "ripple" — tukokno kelas siji lan sepuluh liyane rusak; coupling kendor ndadekke owah mung ing sumberane.

Cohesion dhuwur nggawe kode gampang ditemokake lan bisa ditest: nalika kelas nggarap bab siji, kowe ngerti ana endi logika lan apa sing kudu ditestake.

Rong metrik iki dadi landasan sakabehe prinsip design liyane.