import java.util.ArrayList;
import java.util.List;

public class GenericsExample {
    public static void main(String[] args) {
        // Type-safe collection
        List<String> stringList = new ArrayList<>();
        stringList.add("Hello");
        stringList.add("World");

        // No casting required
        String first = stringList.get(0);
        System.out.println(first);
    }
}

public class Box<T> {
    private T content;

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

    public T getContent() {
        return content;
    }

    // Generic method
    public <U> void inspect(U item) {
        System.out.println("Box contains: " + content);
        System.out.println("Inspecting: " + item);
    }
}

public class GenericMethods {
    // Generic method with bounded type parameter
    public static <T extends Number> double sum(List<T> numbers) {
        double total = 0.0;
        for (T number : numbers) {
            total += number.doubleValue();
        }
        return total;
    }

    // Wildcards for flexible method parameters
    public static void printList(List<?> list) {
        for (Object item : list) {
            System.out.println(item);
        }
    }
}

import java.util.List;

public class WildcardExample {
    // Upper bounded wildcard - can read but not write
    public static double calculateTotal(List<? extends Number> numbers) {
        double total = 0.0;
        for (Number num : numbers) {
            total += num.doubleValue();
        }
        return total;
    }

    // Lower bounded wildcard - can write but limited reading
    public static void addNumbers(List<? super Integer> list) {
        list.add(1);
        list.add(2);
        list.add(3);
    }
}