Add lab6

lab/lab6/Question4/Square.java

@@ -0,0 +1,28 @@
+/*
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
+ * Date: 2022/03/27
+ * Description: Square class
+ */
+
+public class Square extends Rectangle {
+	/**
+	 * Constructor
+	 *
+	 * @param x    the x coordinate of the center of the square
+	 * @param y    the y coordinate of the center of the square
+	 * @param size
+	 */
+	public Square(double x, double y, double size) {
+		super(x, y, size, size);
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testSquare() {
+		Square s = new Square(1.0, 2.0, 3.0);
+		System.out.println(s.getX() == 1.0);
+		System.out.println(s.getY() == 2.0);
+		System.out.println(s.area() == 9.0);
+	}
+}