Je muundo gani wa kawaida unaojitokeza katika Java?

Question

Accepted Answer

**Muundo wa muundo** ni suluhisho zinazotumiwa tena kwa matatizo ya muundo wa programu inayorudiwa. Hadi ya Java inayozingatia OOP na ekosistemu yake hufanya muundo kadhaa kuwa ya kawaida sana — kujua ni kusaidia kukamata, kuwasiliana, na kutumia miundo iliyothibitika. Inakamatia miundo ya uundaji, miundo ya muundo, na miundo ya tabia.

## Singleton (kuundwa) — mfano mmoja unaoshirikiana

```java
public class Config {
    private static final Config INSTANCE = new Config();   // the single instance
    private Config() {}                                     // private constructor
    public static Config getInstance() { return INSTANCE; }
}
// (enum singletons are an even safer idiom). Used for shared config, connection pools.
```

## Factory (kuundwa) — kufunika uundaji wa kitu

```java
public static Shape createShape(String type) {
    return switch (type) {                 // hides the concrete class from the caller
        case "circle" -> new Circle();
        case "square" -> new Square();
        default -> throw new IllegalArgumentException();
    };
}
// caller depends on Shape, not concrete classes — decoupling.
```

## Builder (kuundwa) — jenga vitu tata hatua kwa hatua

```java
User user = new User.Builder()
    .name("Ann")
    .email("ann@x.com")
    .age(30)
    .build();    // readable construction; avoids huge telescoping constructors
```

## Strategy (tabia) — algorithms inayobadilishwa

```java
interface PaymentStrategy { void pay(double amount); }
class CreditCard implements PaymentStrategy { public void pay(double a) {...} }
class PayPal implements PaymentStrategy { public void pay(double a) {...} }

// swap behavior at runtime — lambdas make this trivial in modern Java
processor.setStrategy(new PayPal());
```

## Observer (tabia) — kuchapisha/kujitolea

```java
// subjects notify registered observers of changes (events, listeners)
button.addActionListener(e -> handleClick());   // GUI events use this everywhere
```

## Decorator (miundo ya muundo) — kushughulikia kuongeza tabia

```java
// Java's I/O streams ARE the decorator pattern:
BufferedReader r = new BufferedReader(new FileReader("f.txt"));
// BufferedReader wraps FileReader, adding buffering
```

## Mahali muundo unaojitokeza katika Java yenyewe

```text
Singleton  → Runtime.getRuntime()
Factory    → Calendar.getInstance(), DriverManager
Builder    → StringBuilder, Stream.Builder
Observer   → event listeners, java.util.Observer
Decorator  → java.io streams (BufferedReader wrapping FileReader)
Iterator   → the Iterator interface / Collections
Strategy   → Comparator, functional interfaces
```

## Onyo dhidi ya matumizi yanayozidi

```text
Patterns are tools, not goals. Applying them where they don't fit ADDS complexity.
Use them when they genuinely solve your problem — many can be simpler with lambdas now.
```

## Kwa nini ina maana

Miundo ya muundo inatoa kamusi iliyoshirikiwa na suluhisho zilizothibitika kwa matatizo ya muundo ya kawaida, ambayo ni muhimu kwa mawasiliano ("tumia Strategy hapa"), kutambua miundo katika nambari iliyopo, na kuepuka kufanya upya suluhisho dhaifu.

Inajitokeza katika maktaba yote ya Java (I/O decorators, njia za kiwanda, wajenzi, matukio yanayohusiana na observer), kwa hivyo kuelewa ni kusaidia kutumia na kupanua maktaba ya kawaida kwa ufanisi.

Kujua miundo kuu — Singleton, Factory, Builder, Strategy, Observer, Decorator — na mahali kila mmoja anakokaa ni sifa ya watengenezaji wenye uzamili na mada ya kawaida katika mahojiano.

Kwa njia hiyo pia ni wazi mahakama ya kuyatumia kwa mujibu (kutatua matatizo halisi) badala ya kulazimisha ndani, hasa kama sifa za kisasa kama lambdas kurahisisha muundo mingi ya kawaida.