Add Home interface, Cottage and Flat classes, add App class

Complete interfaces homework main task.

java-oop-ru/interfaces/src/main/java/exercise/App.java

@@ -1,8 +1,15 @@
 package exercise;
 
-import java.util.List;
-import java.util.stream.Collectors;
-
 // BEGIN
+import java.util.List;
 
+public class App {
+    public static List<String> buildApartmentsList(List<Home> apartments, int numOfElements) {
+        return apartments.stream()
+                .sorted(Home::compareTo)
+                .limit(numOfElements)
+                .map(Home::toString)
+                .toList();
+    }
+}
 // END

java-oop-ru/interfaces/src/main/java/exercise/Cottage.java

@@ -1,5 +1,31 @@
 package exercise;
 
 // BEGIN
+import static java.lang.Math.signum;
 
+public class Cottage implements Home{
+    private double area;
+    private int floor;
+
+    public Cottage(double area, int floor) {
+        this.area = area;
+        this.floor = floor;
+    }
+
+    public double getArea() {
+        return this.area;
+    }
+
+    public int compareTo(Home another) {
+        return (int) signum(this.getArea() - another.getArea());
+    }
+
+    @Override
+    public String toString() {
+        return this.floor +
+                " этажный коттедж площадью " +
+                this.getArea() +
+                " метров";
+    }
+}
 // END

java-oop-ru/interfaces/src/main/java/exercise/Flat.java

@@ -1,5 +1,34 @@
 package exercise;
 
 // BEGIN
+import static java.lang.Math.signum;
 
+public class Flat implements Home {
+    private double area;
+    private double balconyArea;
+    private int floor;
+
+    public Flat(double area, double balconyArea, int floor) {
+        this.area = area;
+        this.balconyArea = balconyArea;
+        this.floor = floor;
+    }
+
+    public double getArea() {
+        return this.area + this.balconyArea;
+    }
+
+    public int compareTo(Home another) {
+        return (int) signum(this.getArea() - another.getArea());
+    }
+
+    @Override
+    public String toString() {
+        return "Квартира площадью " +
+                this.getArea() +
+                " метров на " +
+                this.floor +
+                " этаже";
+    }
+}
 // END

java-oop-ru/interfaces/src/main/java/exercise/Home.java

@@ -1,5 +1,8 @@
 package exercise;
 
 // BEGIN
-
+public interface Home {
+    double getArea();
+    int compareTo(Home another);
+}
 // END