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+## Exercises I: Filter
+
+#### Summary
+* The most difficult part for me was to add libraries to **the existing gradle project**. 
+For a long time Junit5 and Hamcrest were not visible. 
+Apparently neither getting them directly via IntelliJ, nor downloading and linking jar files are enough. 
+Gradle has to be built correctly :)
+* I know that code inputs do not look very nice, but this is the best I managed. 
+Code works, this is important :)
+
+#### RectangleArrayProcessor - Implementation of the following methods:
+* **removeRectanglesLargerThan**
+  * takes a Rectangle array and an int n 
+  * returns an array containing only the rectangles with a smaller area than n  
+  * ```java
+    public Rectangle[] removeRectanglesLargerThan(Rectangle[] array, int maxArea) {
+        ArrayList<Rectangle> resultArray = new ArrayList<>();
+        for (Rectangle rectangle: array)
+            if (rectangle.area() <= maxArea)
+                resultArray.add(rectangle);
+        return resultArray.toArray(new Rectangle[resultArray.size()]);
+    }
+    ```
+* **removeRectanglesLargerThan**
+  * takes a Rectangle array and a Rectangle r
+  * returns an array containing only the rectangles with a smaller area than r's area
+  * ```java
+    public Rectangle[] removeRectanglesLargerThan(Rectangle[] array, Rectangle r) {
+        ArrayList<Rectangle> resultArray = new ArrayList<>();
+        for (Rectangle rectangle: array)
+            if (rectangle.compareTo(r) < 0)
+                resultArray.add(rectangle);
+        return resultArray.toArray(new Rectangle[resultArray.size()]);
+    }
+    ```
+* **containsSquare** 
+  * takes a Rectangle array
+  * returns true if the array contains a square or false otherwise
+  * ```java
+    public boolean containsSquare(Rectangle[] array) {
+        for (Rectangle rectangle: array)
+            if (rectangle.getHeight() == rectangle.getWidth())
+                return true;
+        return false;
+    }
+    ```
+* **filterRectanglesWithEqualArea**
+  * takes a Rectangle array and a Rectangle r
+  * returns an array containing only the rectangles with an area equal to r's area
+  * ```java
+    public Rectangle[] filterRectanglesWithEqualArea(Rectangle[] array, Rectangle r) {
+        ArrayList<Rectangle> resultArray = new ArrayList<>();
+        for (Rectangle rectangle: array)
+            if (rectangle.compareTo(r) == 0)
+                resultArray.add(rectangle);
+        return resultArray.toArray(new Rectangle[resultArray.size()]);
+    }
+    ```
+
+#### RectangleArrayProcessorTest - Implementation of the following test methods:
+* **removeRectanglesLargerThan** (both, with input int and Rectangle)
+   ```java
+    @Test
+    void testProcessorRemovesRectanglesLargerThan() {
+        // Arrange
+        Rectangle[] inputArray = {
+                new Rectangle(2, 2),
+                new Rectangle(2, 3),
+                new Rectangle(5, 4),
+                new Rectangle(1, 5)
+        };
+        int inputMaxArea = 5;
+        Rectangle[] expectedArrayForMaxArea = {
+                new Rectangle(2, 2),
+                new Rectangle(1, 5)
+        };
+        Rectangle r = new Rectangle(4, 4);
+        Rectangle[] expectedArrayForR = {
+                new Rectangle(2, 2),
+                new Rectangle(2, 3),
+                new Rectangle(1, 5)
+        };
+
+        // Act
+        Rectangle[] actualArrayForMaxArea = rectangleArrayProcessor.removeRectanglesLargerThan(inputArray, inputMaxArea);
+        Rectangle[] actualArrayForR = rectangleArrayProcessor.removeRectanglesLargerThan(inputArray, r);
+
+        // Assert
+        assertArrayEquals(expectedArrayForMaxArea, actualArrayForMaxArea);
+        assertArrayEquals(expectedArrayForR, actualArrayForR);
+        assertNotEquals(actualArrayForR, actualArrayForMaxArea);
+    }
+    ```
+* **containsSquare** 
+   ```java
+    @Test
+    void testContainsSquare() {
+        // Arrange
+        Rectangle[] inputArrayWithSquare = {
+                new Rectangle(2, 2),
+                new Rectangle(2, 3),
+                new Rectangle(5, 4),
+                new Rectangle(1, 5)
+        };
+        Rectangle[] inputArrayWithoutSquare = {
+                new Rectangle(2, 3),
+                new Rectangle(5, 4),
+                new Rectangle(1, 5)
+        };
+
+        // Act
+        boolean checkOfArrayWithSquare = rectangleArrayProcessor.containsSquare(inputArrayWithSquare);
+        boolean checkOfArrayWithoutSquare = rectangleArrayProcessor.containsSquare(inputArrayWithoutSquare);
+
+        // Assert
+        assertTrue(checkOfArrayWithSquare);
+        assertFalse(checkOfArrayWithoutSquare);
+    }
+    ```
+* **filterRectanglesWithEqualArea**
+   ```java
+    @Test
+    void testFilterRectanglesWithEqualArea() {
+        // Arrange
+        Rectangle[] inputArrayWith = {
+                new Rectangle(2, 2),
+                new Rectangle(2, 3),
+                new Rectangle(5, 4),
+                new Rectangle(3, 2),
+                new Rectangle(1, 6),
+                new Rectangle(5, 3),
+                new Rectangle(3, 5)
+        };
+        Rectangle[] inputArrayWithout = {
+                new Rectangle(2, 2),
+                new Rectangle(5, 4),
+                new Rectangle(5, 3),
+                new Rectangle(3, 5)
+        };
+        Rectangle r = new Rectangle(6, 1);
+        Rectangle[] expectedArrayWithForR = {
+                new Rectangle(2, 3),
+                new Rectangle(3, 2),
+                new Rectangle(1, 6),
+        };
+
+        // Act
+        Rectangle[] actualArrayWithForR = rectangleArrayProcessor.filterRectanglesWithEqualArea(inputArrayWith, r);
+        int actualSizeArrayWithoutForR = rectangleArrayProcessor.filterRectanglesWithEqualArea(inputArrayWithout, r).length;
+
+        // Assert
+        assertArrayEquals(expectedArrayWithForR, actualArrayWithForR);
+        assertEquals(0, actualSizeArrayWithoutForR);
+    }
+    ```