المنشئات المختصرة والتحقق

المنشئات المختصرة

المنشئ القياسي مقارنةً بالمنشئ المختصر

// Standard canonical constructor
record Range(int min, int max) {
    Range(int min, int max) {
        if (min > max) throw new IllegalArgumentException("min > max");
        this.min = min;  // explicit assignment
        this.max = max;
    }
}

// Compact constructor (same behavior, less code)
record Range2(int min, int max) {
    Range2 {  // no parameter list, no assignments
        if (min > max) throw new IllegalArgumentException("min > max");
        // components are assigned automatically after this block
    }
}

التحقق في المنشئات المختصرة

record Email(String address) {
    Email {
        if (address == null || address.isBlank())
            throw new IllegalArgumentException("Email cannot be blank");
        if (!address.contains("@"))
            throw new IllegalArgumentException("Invalid email: " + address);
        address = address.toLowerCase().strip(); // normalize (Java 16+)
    }
}

Email e = new Email("  Alice@Example.com  ");
System.out.println(e.address()); // alice@example.com

try { new Email("not-an-email"); }
catch (IllegalArgumentException ex) { System.out.println(ex.getMessage()); }

التطبيع في المنشئات المختصرة

record PersonName(String firstName, String lastName) {
    PersonName {
        firstName = capitalize(firstName);
        lastName  = capitalize(lastName);
    }

    private static String capitalize(String s) {
        if (s == null || s.isEmpty()) return s;
        return Character.toUpperCase(s.charAt(0)) +
               s.substring(1).toLowerCase();
    }

    public String fullName() { return firstName + " " + lastName; }
}

PersonName name = new PersonName("jOHN", "DOE");
System.out.println(name.fullName()); // John Doe

النسخ الوقائي

import java.util.*;

record Snapshot(List<String> items) {
    Snapshot {
        items = List.copyOf(items); // defensive copy — unmodifiable
    }
}

List<String> mutable = new ArrayList<>(List.of("a", "b", "c"));
Snapshot snap = new Snapshot(mutable);
mutable.add("d"); // doesn't affect snapshot
System.out.println(snap.items()); // [a, b, c]

try {
    snap.items().add("e"); // UnsupportedOperationException
} catch (UnsupportedOperationException e) {
    System.out.println("Snapshot is truly immutable!");
}

سجل Range بحدود

record Range(int min, int max) {
    Range {
        if (min > max) throw new IllegalArgumentException(
            "min (" + min + ") must be <= max (" + max + ")");
    }

    public boolean contains(int value) { return value >= min && value <= max; }
    public int size()  { return max - min; }
    public int clamp(int value) { return Math.max(min, Math.min(max, value)); }
}

Range valid = new Range(1, 10);
System.out.println(valid.contains(5));  // true
System.out.println(valid.clamp(15));    // 10
System.out.println(valid.size());       // 9

تسلسل منطق المنشئ المختصر

record CreditCard(String number, String cvv, int expiryMonth, int expiryYear) {
    CreditCard {
        validateNumber(number);
        validateCvv(cvv);
        validateExpiry(expiryMonth, expiryYear);
        number = number.replaceAll("[^0-9]", ""); // strip spaces/dashes
    }

    private static void validateNumber(String n) {
        String digits = n.replaceAll("[^0-9]", "");
        if (digits.length() < 13 || digits.length() > 19)
            throw new IllegalArgumentException("Invalid card number length");
    }
    private static void validateCvv(String cvv) {
        if (!cvv.matches("[0-9]{3,4}"))
            throw new IllegalArgumentException("Invalid CVV");
    }
    private static void validateExpiry(int m, int y) {
        if (m < 1 || m > 12) throw new IllegalArgumentException("Invalid month");
        if (y < 2024)         throw new IllegalArgumentException("Card expired");
    }
}

أنماط متعددة للمنشئات المختصرة

record Percentage(double value) {
    Percentage {
        if (value < 0 || value > 100)
            throw new IllegalArgumentException(
                "Percentage must be 0-100, got: " + value);
        value = Math.round(value * 100.0) / 100.0; // round to 2 dp
    }

    public double asFraction() { return value / 100.0; }
}

Percentage tax = new Percentage(8.756);
System.out.println(tax.value());       // 8.76
System.out.println(tax.asFraction()); // 0.0876

المنشئات غير الأساسية

record Point(double x, double y) {
    // Non-canonical constructor: origin point
    Point() { this(0.0, 0.0); }

    // Non-canonical: polar coordinates
    static Point fromPolar(double r, double theta) {
        return new Point(r * Math.cos(theta), r * Math.sin(theta));
    }

    public double distance(Point other) {
        double dx = this.x - other.x;
        double dy = this.y - other.y;
        return Math.sqrt(dx*dx + dy*dy);
    }
}

Point origin = new Point();
Point p = Point.fromPolar(5, Math.PI/4);
System.out.printf("Distance: %.2f%n", origin.distance(p)); // 5.00

سجل مجموعة غير قابلة للتغيير

import java.util.*;

record UserPreferences(String theme, Set<String> enabledFeatures, int fontSize) {
    private static final Set<String> VALID_THEMES = Set.of("light", "dark", "system");
    private static final Set<String> VALID_FEATURES = Set.of("ai", "beta", "analytics");

    UserPreferences {
        if (!VALID_THEMES.contains(theme))
            throw new IllegalArgumentException("Unknown theme: " + theme);
        if (!VALID_FEATURES.containsAll(enabledFeatures))
            throw new IllegalArgumentException("Unknown feature in: " + enabledFeatures);
        if (fontSize < 10 || fontSize > 24)
            throw new IllegalArgumentException("fontSize must be 10-24");
        enabledFeatures = Set.copyOf(enabledFeatures); // defensive copy
    }
}

قيود المنشئات المختصرة

record Safe(int value) {
    Safe {
        // CAN: validate and modify component variables
        if (value < 0) value = 0; // normalized to 0 if negative
        // value = this.value; // NOT NEEDED — assignment happens after block
    }
}

System.out.println(new Safe(-5).value());  // 0 (normalized)
System.out.println(new Safe(10).value());  // 10

اختبار سريع

مراجعة: المنشئات المختصرة والتحقق