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黑墨水鱼
2022-04-17 11:41:41 +08:00
parent fdb4e8296d
commit cea6585033
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59
lab/lab8/Question3/Circle.java Normal file
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/*
* Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
* Date: 2022-04-14
* Description: Circle class inherit from Shape class
*/
public class Circle extends Shape {
private double radius;
/**
* Constructor.
*
* @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;
}
/**
* Calculates the area of the circle.
*
* @return the area of the circle
*/
@Override
public double area() {
return Math.PI * radius * radius;
}
/**
* Resizing a circle cahnges its radius to be newRadius.
*
* @param newRadius
*/
@Override
public void resize(double newRadius) {
radius = newRadius;
}
/**
* Test.
*/
public static void testCircle() {
Circle c1 = new Circle(1.0, 2.0, 3.0);
System.out.println(c1.area() == Math.PI * 9.0);
System.out.println(c1.getX() == 1.0);
System.out.println(c1.getY() == 2.0);
c1.resize(4.0);
System.out.println(c1.area() == Math.PI * 16.0);
System.out.println(c1.getX() == 1.0);
System.out.println(c1.getY() == 2.0);
c1.move(5.0, 6.0);
System.out.println(c1.area() == Math.PI * 16.0);
System.out.println(c1.getX() == 6.0);
System.out.println(c1.getY() == 8.0);
}
}

64
lab/lab8/Question3/Dot.java Normal file
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/*
* Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
* Date: 2022-04-14
* Description: This is the Dot class inherited from Shape class.
*/
public class Dot extends Shape {
/**
* Constructor.
*
* @param x the x coordinate of the dot
* @param y the y coordinate of the dot
*/
public Dot(double x, double y) {
super(x, y);
}
/**
* Calculates the dot's area.
*
* @return the area of the dot
*/
public double area() {
return 0;
}
/**
* Resize method of Dot throw an Exception with message "Cannot resize a dot!"
*
* @param newSize the new size of the dot
* @throws Exception the exception
*/
@Override
public void resize(double newSize) throws Exception {
throw new Exception("Cannot resize a dot!");
}
/**
* Test.
*/
public static void testDot() {
Dot d = new Dot(1.2, 3.4);
// getX, getY, and move are inherited from Shape.
// area and resize come from Dot itself.
System.out.println(d.getX() == 1.2);
System.out.println(d.getY() == 3.4);
System.out.println(d.area() == 0.0);
// Move the dot. The area does not change.
d.move(7.8, 9.0);
System.out.println(d.getX() == 9.0);
System.out.println(d.getY() == 12.4);
System.out.println(d.area() == 0.0);
// Resize the dot. An exception is thrown, caught, and tested.
try {
d.resize(12.3);
} catch (Exception ex) {
System.out.println(ex.getMessage() == "Cannot resize a dot!");
}
// The area and position do not change.
System.out.println(d.getX() == 9.0);
System.out.println(d.getY() == 12.4);
System.out.println(d.area() == 0.0);
}
}

89
lab/lab8/Question3/Shape.java Normal file
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/*
* Author: CHEN Yongyuan (Walter) 1930006025 from OOP(1007)
* Date: 2022-04-15
* Description: This is the abstract Shape class.
*/
public abstract class Shape {
/*
* Store the position of the central point of the shape.
*/
private double x;
private double y;
/**
* Constructor of the Shape class.
*
* @param x the x-coordinate of the central point of the shape.
* @param y the y-coordinate of the central point of the shape.
*/
public Shape(double x, double y) {
this.x = x;
this.y = y;
}
/**
* Getter of the x coordinate of the central point of the shape.
*
* @return the x coordinate of the central point of the shape.
*/
public double getX() {
return x;
}
/**
* Getter of the y coordinate of the central point of the shape.
*
* @return the y coordinate of the central point of the shape.
*/
public double getY() {
return y;
}
/**
* Move the central point of the shape by amounts dx and dy.
*
* @param dx the amount of movement in x direction.
* @param dy the amount of movement in y direction.
*/
public void move(double dx, double dy) {
x += dx;
y += dy;
}
/**
* Abstract method to calculate the area of the shape.
*
* @return the area of the shape.
*/
public abstract double area();
/**
* Abstract method to resize the shape.
*
* @param newSize the new size of the shape.
* @throws Exception
*/
public abstract void resize(double newSize) throws Exception;
/**
* Test.
*/
public static void testShape() {
Shape s = new Shape(3.9, 4.2) {
@Override
public double area() {
return 0;
}
@Override
public void resize(double newSize) {
}
};
System.out.println(s.getX() == 3.9);
System.out.println(s.getY() == 4.2);
s.move(1.0, 2.0);
System.out.println(s.getX() == 4.9);
System.out.println(s.getY() == 6.2);
}
}

24
lab/lab8/Question3/Start.java Normal file
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/**
* Answers the question.
*
* Question3:
*
* - Q: What is the problem with the resize method of the Shape calss? How do
* you solve this problem?
*
* - A: The resize method of the Dot class is inherited from the Shape class.
* which does not have a throw Exception declared. We can solve this problem by
* declaring the resize method in the Shape class as a throw Exception.
*
* - Q: Do you need to change the resize method of the Circle class then?
*
* - A: No, we do not need to change the resize method of the Circle class.
*/
public class Start {
public static void main(String[] args) {
Shape.testShape();
Circle.testCircle();
Dot.testDot();
}
}