Kalade, abubuwa, da masu gida suna aiki ta yaya?

Question

Accepted Answer

**Ajiya** ita ce zukin nisa; **wani abu** ita ce misali da aka samu daga ita. **Mai gida** ita ce wata hanya ta musamman da ke haɗawa da sabon wani abu. Juna gida, su ne tushen Java ikon da aka tsara.

## Bayyana ajiya tare da mai gida

```java
public class Person {
    private String name;        // fields (instance variables)
    private int age;

// CONSTRUCTOR — same name as the class, no return type
    public Person(String name, int age) {
        this.name = name;       // `this` distinguishes field from parameter
        this.age = age;
    }

public String greet() {     // method
        return "Hi, I'm " + name;
    }
}
```

Mai gida yana aiki lokacin da kake yin wani abu, sai ya saje ga asusunsa na farko. `this` yana nufin wani abu na yanzu, yana bayyana fage daga ma'auni da kama jiya.

## Yin abubuwa

```java
Person p = new Person("Ann", 30);   // `new` allocates the object + calls the constructor
p.greet();                           // "Hi, I'm Ann"
```

`new` furannin yana ƙayyade ƙarfi akan tuƙi kuma yana kira mai gida; `p` yana riƙe da haɗin ga sabon wani abu.

## Kori gari da jujjuyawar masu gida

```java
public class Person {
    private String name;
    private int age;

public Person(String name, int age) {   // primary constructor
        this.name = name;
        this.age = age;
    }
    public Person(String name) {             // overloaded — different parameters
        this(name, 0);                        // calls the other constructor (chaining)
    }
}
```

Kun yi **masu gida da da yawa** tare da jerin sinaɗi daban-daban (kori gari), kuma ɗaya zai iya kira wani tare da `this(...)` don guje wa juya haɗawa.

## Mai gida na asusun ƙasua

```java
public class Empty {
    // no constructor defined → Java provides an implicit no-arg constructor
}
Empty e = new Empty();   // works
// BUT: once you define ANY constructor, the implicit one is gone
```

Ida ba ka rubuta wani mai gida, Java yana ba da asusun ƙasua ba tare da jiya. Da leɗi ka bayyana wani mai gida, waccan asusun ƙasua ta baci (dole ne ka ƙara shi da bayyani idan aka buƙata).

## Me yasa hakan mahimmaci

Ajiya, abubuwa, da masu gida su ne tushen cikakken Java shirye - kome da kake gina yana kira abubuwa da aka yin daga ajiya.

Sanin ta yaya masu gida ke haɗawa asusun (`this`, rolin `new` furannin, kori gari da jujjuyawar masu gida don yin ƙayyade da dandali, da ƙa'idar asusun ƙasua mai gida) ya zama dole don daidai yin da haɗawa abubuwa.

Wadannan tunani sun danganta da duka aikin OOP a Java, kuma halayen mai gida (musamman asusun ƙasua ta baci da jujjuyawa) shine kira gida na tambayoyi na jiya da bugs na gaske.