Add lab6

lab/lab6/Question3/Circle.java

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+/**
+ * Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007) Date: 2022/03/27
+ * Description: This is the class of Circle.
+ */
+
+public class Circle extends Shape {
+	private double radius;
+
+	/**
+	 * Constructor of Circle.
+	 *
+	 * @param x      the x coordinate of the center of the circle
+	 * @param y      the y coordinate of the center of the circle
+	 * @param radius the radius of the circle
+	 */
+	public Circle(double x, double y, double radius) {
+		super(x, y);
+		this.radius = radius;
+	}
+
+	/**
+	 * Get the area of the circle.
+	 *
+	 * @return the area of the circle
+	 */
+	@Override
+	public double area() {
+		return Math.PI * radius * radius;
+	}
+
+	/**
+	 * Test
+	 */
+	public static void testCircle() {
+		Circle c1 = new Circle(1.0, 2.0, 3.0);
+		System.out.println(c1.getX() == 1.0);
+		System.out.println(c1.getY() == 2.0);
+		System.out.println(compare(c1.area(), 28.274333882308138));
+	}
+
+	/**
+	 * Compare two double numbers.
+	 *
+	 * @param a
+	 * @param b
+	 * @return true if a and b are equal, false otherwise
+	 */
+	public static boolean compare(double a, double b) {
+		return Math.abs(a - b) < 0.000001;
+	}
+}