Bayyana Lokacin Liskov Substitution Principle a jiki.

Question

Accepted Answer

**Lokacin Liskov Substitution Principle (LSP)** ya bayyana cewa abubuwan subtype dole ne su kafaru abin ginawa na tsararren **ba tare da karya jiya ta programa ba**. Idan lambar ta aiki da `Base`, dole ne ta aiki da wani `Subclass` — inazo matakin jiyya, ba wani surpresa.

## Me yake sa'a

```java
class Rectangle {
    protected int w, h;
    void setWidth(int w)  { this.w = w; }
    void setHeight(int h) { this.h = h; }
    int area() { return w * h; }
}

class Square extends Rectangle {       // "a square IS-A rectangle"... seemingly
    void setWidth(int w)  { this.w = w; this.h = w; }   // keep sides equal
    void setHeight(int h) { this.w = h; this.h = h; }
}

void resize(Rectangle r) {
    r.setWidth(5);
    r.setHeight(4);
    assert r.area() == 20;   // holds for Rectangle... FAILS for Square (area=16)
}
```

`Square` *ya furaici alkawari* masu dogaro: saita fadi da tsayi ba kamar ɗaya ba. Ya wuce gwajin "is-a" na Turanci amma **ya saba lokacin LSP**.

## Abin da LSP suke bukatu gaske gaske

```text
A subtype must NOT:
  ✗ strengthen preconditions  (demand more than the base, e.g. reject valid inputs)
  ✗ weaken postconditions     (promise less than the base)
  ✗ break invariants the base guarantees
  ✗ throw new unexpected exceptions for previously valid calls
A subtype MAY:
  ✓ weaken preconditions (accept more)   ✓ strengthen postconditions (promise more)
```

Yan hanyar da **contravariance na abubuwan shigarwa, covariance na abubuwan fitarwa** — gida na LSP.

## Yadda za a gyara misal

Bari gida: `Square` da `Rectangle` duk `Shape`s ne tare da `area()`, amma ba ɗaya ba ce. Tsara jiyya, ba naive taxonomy.

## Me yake sa'a

LSP ne abin da ya sa polymorphism *aminci*: ba tare da shi, kowane shawara `if (x instanceof Square)` ya koma jiya, ta karya tamkar ginawa na subtyping.

Ya sake fasalin hankalin gida in kewaye da **alkawari jiyya**, ba kalmomi ba — ainihin dalili ta-ne "fito composition" ya kasance wa-shi wadanda da yawa is-a alaƙa ta saba LSP cikin shiru.