Ni nini tofauti kati ya mahusiano ya is-a na has-a?

Question

IT Interview Practice · Accepted Answer

**Is-a** ni mahusiano ya *aina* — yaonekanwa kwa **urithi** (kitu `Car` *ni* `Vehicle`). **Has-a** ni mahusiano ya *kuwa na* — yaonekanwa kwa **composition** (kitu `Car` *kina* `Engine`). Kuchagua kitanzi sahihi ni uamuzi muhimu wa kuiga.

## Mahusiano mawili

```java
// IS-A → inheritance
class Vehicle { void move() {} }
class Car extends Vehicle { }        // a Car IS A Vehicle

// HAS-A → composition
class Engine { void start() {} }
class Car2 {
    private Engine engine = new Engine();   // a Car HAS AN Engine
    void start() { engine.start(); }        // delegate to the part
}
```

## Mtihani wa kawaida

Uliza: "Je, X *ni aina ya* Y, au X *ina/hutumia* Y?"

```text
A Dog        IS-A Animal        → inheritance ✅
A Car        HAS-A Engine       → composition ✅
A Square     IS-A Shape         → inheritance ✅
A Manager    HAS Employees      → composition (a list) ✅
A Stack      HAS-A list (not IS-A) → composition (see earlier pitfall) ✅
```

## Ndoto

Watu wanakaribiana na urithi ili *kutumia tena kod*, hata wakati mahusiano yaliyoo ni has-a. Ikiwa haungekuwa na njia ya kubadili darasa dogo kwa msingi kila mahali, labda si is-a — tumia composition.

## Kwa nini ni muhimu

Tofauti hii ni sheria ya uamuzi wa vitendo nyuma ya "pendekeza composition juu ya urithi": chagua mahusiano yanayotaka, si ile inayookoa mistari michache.

Kupata kazi sawa inahifadhi hierarchies nyingi na adimu, na inazuia ukiukaji wa Liskov ambapo "subtype" haiwezi kweli kusimama mahali pa mzazi wake.

Mahusiano mawili

Mtihani wa kawaida

Ndoto

Kwa nini ni muhimu

Maswali yanayohusiana