Interview question

How do you create a generic class in Java? Java में generic class कैसे बनाएं?

Answer

// Generic class with a single type parameter T
class Box<T> {
    private T content;

    public void set(T content) {
        this.content = content;
    }

    public T get() {
        return content;
    }
}

Box<String> stringBox = new Box<>();
stringBox.set('Hello');
String value = stringBox.get();  // no cast needed

Box<Integer> intBox = new Box<>();
intBox.set(42);
Integer num = intBox.get();

// Generic class with MULTIPLE type parameters
class Pair<K, V> {
    private K key;
    private V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() { return key; }
    public V getValue() { return value; }
}

Pair<String, Integer> pair = new Pair<>('age', 30);
System.out.println(pair.getKey() + ': ' + pair.getValue());  // age: 30

// Common type parameter naming conventions:
// T - Type, E - Element, K - Key, V - Value, N - Number, R - Return type

// Generic class can have bounded type parameters too
class NumericBox<T extends Number> {
    private T value;
    public void set(T value) { this.value = value; }
    public double doubleValue() { return value.doubleValue(); }  // Number methods available
}

// एक type parameter वाली generic class
class Box<T> {
    private T content;

    public void set(T content) {
        this.content = content;
    }

    public T get() {
        return content;
    }
}

Box<String> stringBox = new Box<>();
stringBox.set('Hello');
String value = stringBox.get();

Box<Integer> intBox = new Box<>();
intBox.set(42);

// Multiple type parameters वाली generic class
class Pair<K, V> {
    private K key;
    private V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() { return key; }
    public V getValue() { return value; }
}

Pair<String, Integer> pair = new Pair<>('age', 30);
System.out.println(pair.getKey() + ': ' + pair.getValue());

// Naming conventions: T, E, K, V, N, R

class NumericBox<T extends Number> {
    private T value;
    public void set(T value) { this.value = value; }
    public double doubleValue() { return value.doubleValue(); }
}

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