الفئات المحلية والمجهولة

الفئات المحلية والمجهولة

تصريح الفئة المحلية

static void greet(String language) {
    // Local class — defined inside the method
    class Greeter {
        String sayHello(String name) {
            // Can access 'language' — it is effectively final
            return switch (language) {
                case "EN" -> "Hello, " + name;
                case "ES" -> "Hola, " + name;
                case "FR" -> "Bonjour, " + name;
                default   -> "Hi, " + name;
            };
        }
    }

    Greeter g = new Greeter();
    System.out.println(g.sayHello("Alice"));
}
greet("ES"); // Hola, Alice

المتغيرات النهائية فعليًا

void process(int threshold) {
    // threshold is effectively final (never reassigned)
    Runnable r = new Runnable() {
        public void run() {
            System.out.println("Threshold: " + threshold);
        }
    };
    r.run();

    // threshold = 10; // If you add this, the anonymous class won't compile
}

أساسيات الفئات المجهولة

interface Comparator<T> {
    int compare(T a, T b);
}

// Anonymous class implementing Comparator
java.util.Comparator<String> byLength = new java.util.Comparator<String>() {
    @Override
    public int compare(String a, String b) {
        return Integer.compare(a.length(), b.length());
    }
};

List<String> words = new ArrayList<>(List.of("banana", "fig", "apple", "kiwi"));
words.sort(byLength);
System.out.println(words); // [fig, kiwi, apple, banana]

الفئة المجهولة مقابل Lambda

// Anonymous class for single-method interface
Runnable r1 = new Runnable() {
    public void run() { System.out.println("Running!"); }
};

// Lambda — cleaner for SAM interfaces
Runnable r2 = () -> System.out.println("Running!");

// Must use anonymous class for multi-method interface:
java.io.FilenameFilter filter = new java.io.FilenameFilter() {
    public boolean accept(java.io.File dir, String name) {
        return name.endsWith(".java");
    }
}; // FilenameFilter is not a SAM — no lambda shorthand

الفئة المجهولة ذات الحالة

interface Counter { int increment(); int get(); }

Counter counter = new Counter() {
    private int count = 0;

    public int increment() { return ++count; }
    public int get()       { return count; }
};

System.out.println(counter.increment()); // 1
System.out.println(counter.increment()); // 2
System.out.println(counter.get());       // 2

نمط المستمع المجهول

// Modern Android/Swing style: anonymous class listener
Button loginButton = new Button(); // hypothetical
loginButton.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick() {
        System.out.println("Login button clicked!");
    }
});

// Modern equivalent with lambda (if OnClickListener is SAM):
loginButton.setOnClickListener(() -> System.out.println("Clicked!"));

الفئة المحلية للمنطق المعقّد

static List<String> processData(List<String> data, String prefix) {
    // Local class: complex enough for a class, used only here
    class DataProcessor {
        List<String> result = new ArrayList<>();

        void process(String item) {
            // prefix is effectively final
            if (item.startsWith(prefix)) {
                result.add(item.toUpperCase());
            }
        }
    }
    DataProcessor dp = new DataProcessor();
    data.forEach(dp::process);
    return dp.result;
}
System.out.println(processData(List.of("apple","avocado","banana"), "a"));
// [APPLE, AVOCADO]

الفئة المجهولة للفئة المجرّدة

abstract class ReportFormatter {
    abstract String formatHeader(String title);
    abstract String formatBody(List<String> rows);

    String format(String title, List<String> rows) {
        return formatHeader(title) + "\n" + formatBody(rows);
    }
}

ReportFormatter csvFormatter = new ReportFormatter() {
    public String formatHeader(String t) { return "\"" + t + "\""; }
    public String formatBody(List<String> rows) {
        return String.join("\n", rows);
    }
};
System.out.println(csvFormatter.format("Sales", List.of("a,1","b,2")));

النمط المضاد للتهيئة ذات القوسين المعقوفين

// Anti-pattern: double-brace initialization
Map<String, Integer> map = new HashMap<String, Integer>() {{
    put("a", 1);
    put("b", 2);
}};
// Creates an anonymous HashMap subclass — wasteful!

// GOOD: use Map.of() or Map.ofEntries()
Map<String, Integer> better = Map.of("a", 1, "b", 2);

// Or a mutable map:
Map<String, Integer> mutable = new HashMap<>(Map.of("a", 1, "b", 2));

الاختيار: Lambda أم فئة مجهولة أم فئة محلية

تحقق سريع

مراجعة: الفئات المحلية والمجهولة