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Advanced Concepts

Explore modern Java features that make your code more powerful and expressive.

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Advanced Concepts

Generics

Generics allow you to write flexible, reusable code that works with different types while maintaining type safety.

Why Use Generics?

// Without generics - not type-safe
ArrayList list = new ArrayList();
list.add("Hello");
list.add(123);
String text = (String) list.get(1);  // Runtime error!

// With generics - type-safe
ArrayList<String> names = new ArrayList<>();
names.add("Alice");
names.add("Bob");
// names.add(123);  // Compile-time error - type safety!
String name = names.get(0);  // No casting needed

Generic Classes

// Generic class with type parameter T
public class Box<T> {
    private T content;
    
    public void set(T content) {
        this.content = content;
    }
    
    public T get() {
        return content;
    }
}

// Usage
public class Main {
    public static void main(String[] args) {
        // Box for String
        Box<String> stringBox = new Box<>();
        stringBox.set("Hello");
        String text = stringBox.get();
        
        // Box for Integer
        Box<Integer> intBox = new Box<>();
        intBox.set(42);
        int number = intBox.get();
        
        // Box for custom objects
        Box<Person> personBox = new Box<>();
        personBox.set(new Person("Alice", 25));
    }
}

Generic Methods

public class GenericMethods {
    // Generic method
    public static <T> void printArray(T[] array) {
        for (T element : array) {
            System.out.print(element + " ");
        }
        System.out.println();
    }
    
    // Generic method with return type
    public static <T> T getFirst(T[] array) {
        if (array.length > 0) {
            return array[0];
        }
        return null;
    }
    
    public static void main(String[] args) {
        Integer[] numbers = {1, 2, 3, 4, 5};
        String[] names = {"Alice", "Bob", "Charlie"};
        
        printArray(numbers);  // 1 2 3 4 5
        printArray(names);    // Alice Bob Charlie
        
        Integer first = getFirst(numbers);
        String firstName = getFirst(names);
    }
}

Bounded Type Parameters

// Upper bound: T must be Number or its subclass
public class Calculator<T extends Number> {
    private T value;
    
    public Calculator(T value) {
        this.value = value;
    }
    
    public double getDoubleValue() {
        return value.doubleValue();
    }
}

// Usage
Calculator<Integer> intCalc = new Calculator<>(42);
Calculator<Double> doubleCalc = new Calculator<>(3.14);
// Calculator<String> stringCalc = new Calculator<>("text");  // Error!