Rectangle.java

public final class Rectangle {
    private final int width;
    private final int height;

    public Rectangle(int width, int height) {
        this.width = width;
        this.height = height;
    }

    public int area() {
        return width * height;
    }

    public int perimeter() {
        return 2 * (width + height);
    }

    public int getWidth() {
        return width;
    }

    public int getHeight() {
        return height;
    }
}

RectangleStats.java

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

public class RectangleStats {
    public static int combinedArea(Collection<Rectangle> rectangles) {
        int sum = 0;
        for (Rectangle rectangle : rectangles) {
            sum += rectangle.area();
        }
        return sum;
    }

    public static int combinedPerimeter(Collection<Rectangle> rectangles) {
        int sum = 0;
        for (Rectangle rectangle : rectangles) {
            sum += rectangle.perimeter();
        }
        return sum;
    }

    public static void main(String[] args) {
        List<Rectangle> rectangles = new ArrayList<>();
        rectangles.add(new Rectangle(10, 5));
        rectangles.add(new Rectangle(4, 3));
        System.out.println("Combined area = " + RectangleStats.combinedArea(rectangles));
        System.out.println("Combined perimeter = " + RectangleStats.combinedPerimeter(rectangles));
    }
}