嘿，我试图弄清楚从子类中的父类访问变量的值。
情景＃1
以下是课程DrawingPanel()的代码：
public class DrawingPanel extends JPanel implements MouseListener
{
private ArrayList<Balloon> balloons;
private Balloon activeBalloon;
private boolean picked;
private int offsetX, offsetY;
private double offsetR;
int rotate;
// Constructor:
public DrawingPanel()
{
setBackground(Color.WHITE);
addMouseListener(this);
balloons = new ArrayList<Balloon>();
activeBalloon = null;
picked = false;
rotate = 0;
}
// Called from controlPanel when the "Add balloon" button is clicked.
// Places a new balloon with a random radius and the current color
// at the center of the drawing panel.
public void addBalloon(int shape)
{
int w = getWidth();
int h = getHeight();
int radius = 10 + (int) (Math.random() * w / 2);
switch (shape)
{
case 1:
activeBalloon = new SquareBalloon(w / 2, h / 2, radius);
break;
default:
activeBalloon = new SquareBalloon(w / 2, h / 2, radius);
break;
}
balloons.add(activeBalloon);
repaint();
}
// Repaints this panel. If activeBalloon is set, paints it on top.
@Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
for (Balloon b : balloons)
{
if (!picked || b != activeBalloon)
{
b.draw(g, true);
}
}
if (picked && activeBalloon != null)
activeBalloon.draw(g, false);
}
// Called when the mouse is clicked on the drawing panel.
// If inside a balloon, makes it "active", remembers the offsets
// of the click from the center.
// If on the border of a balloon, makes it "active", remembers the
// distance of the click from the center.
@Override
public void mousePressed(MouseEvent e)
{
// Value for parameter rotate is set here on mouse click
rotate = 2;
int x = e.getX();
int y = e.getY();
picked = false;
for (int k = balloons.size() - 1; k >= 0 && !picked; k--)
{
Balloon b = balloons.get(k);
if (b.isInside(x, y))
{
picked = true;
offsetX = x - b.getX();
offsetY = y - b.getY();
activeBalloon = b;
} else if (b.isOnBorder(x, y))
{
picked = true;
offsetR = b.distance(x, y) - b.getRadius();
activeBalloon = b;
}
}
if (picked)
repaint();
}
// "Drops" the picked balloon, if any.
@Override
public void mouseReleased(MouseEvent e)
{
}
// Not used:
@Override
public void mouseEntered(MouseEvent e)
{
}
@Override
public void mouseExited(MouseEvent e)
{
}
@Override
public void mouseClicked(MouseEvent e)
{
}
}
以下是继承父类SquareBalloon()的{{1}}类。 Balloon类继承Balloon类。
DrawingPanel()情景＃2
以下是课程public class SquareBalloon extends Balloon implements MouseListener
{
public SquareBalloon()
{
}
/**
* Constructs a balloon with a given center, radius and color
*
* @param x
* x-coordinate of the center
* @param y
* y-coordinate of the center
* @param r
* radius of the balloon
*/
public SquareBalloon(int x, int y, int r)
{
super(x, y, r);
}
/**
* Draws a solid circle if makeItFilled is true and outline only if
* makeItFilled is false
*
* @param g
* graphics context
* @param makeItFilled
* draws a solid circle if true
*/
@Override
public void draw(Graphics g, boolean makeItFilled)
{
Graphics2D g2d = (Graphics2D) g;
g.setColor(color);
System.out.println("This is the value of rotate" + rotate + "from the draw() method of SquareBalloon() class.");
if (makeItFilled)
{
Rectangle rect2 = new Rectangle(xCenter - radius, yCenter - radius, radius, radius);
if (rotate == 2)
{
System.out.println("This is the value of rotate" + rotate
+ "from the makedItFilled if statement in draw() method of SquareBalloon() class.");
g2d.rotate(45 * (Math.PI / 180));
}
g2d.fill(rect2);
} else
{
Rectangle rect2 = new Rectangle(xCenter - radius, yCenter - radius, radius, radius);
if (rotate == 2)
{
System.out.println("This is the value of rotate" + rotate
+ "from the other if statement in draw() method of SquareBalloon() class.");
g2d.rotate(45 * (Math.PI / 180));
}
g2d.draw(rect2);
}
}
}
的代码：
DrawingPanel()以下是继承父类public class DrawingPanel extends JPanel implements MouseListener
{
private ArrayList<Balloon> balloons;
private Balloon activeBalloon;
private boolean picked;
private int offsetX, offsetY;
private double offsetR;
int rotate;
// Constructor:
public DrawingPanel()
{
setBackground(Color.WHITE);
addMouseListener(this);
balloons = new ArrayList<Balloon>();
activeBalloon = null;
picked = false;
rotate = 0;
}
// Called from controlPanel when the "Add balloon" button is clicked.
// Places a new balloon with a random radius and the current color
// at the center of the drawing panel.
public void addBalloon(int shape)
{
int w = getWidth();
int h = getHeight();
int radius = 10 + (int) (Math.random() * w / 2);
switch (shape)
{
case 1:
activeBalloon = new SquareBalloon(w / 2, h / 2, radius);
break;
default:
activeBalloon = new SquareBalloon(w / 2, h / 2, radius);
break;
}
balloons.add(activeBalloon);
repaint();
}
// Repaints this panel. If activeBalloon is set, paints it on top.
@Override
public void paintComponent(Graphics g)
{
// to restore original angle of balloon objects
if (rotate > 2)
rotate = 0;
super.paintComponent(g);
for (Balloon b : balloons)
{
if (!picked || b != activeBalloon)
{
b.draw(g, true, rotate);
}
}
if (picked && activeBalloon != null)
activeBalloon.draw(g, false, rotate);
}
// Called when the mouse is clicked on the drawing panel.
// If inside a balloon, makes it "active", remembers the offsets
// of the click from the center.
// If on the border of a balloon, makes it "active", remembers the
// distance of the click from the center.
@Override
public void mousePressed(MouseEvent e)
{
// Value for parameter rotate is set here on mouse click
rotate++;
int x = e.getX();
int y = e.getY();
picked = false;
for (int k = balloons.size() - 1; k >= 0 && !picked; k--)
{
Balloon b = balloons.get(k);
if (b.isInside(x, y))
{
picked = true;
offsetX = x - b.getX();
offsetY = y - b.getY();
activeBalloon = b;
} else if (b.isOnBorder(x, y))
{
picked = true;
offsetR = b.distance(x, y) - b.getRadius();
activeBalloon = b;
}
}
if (picked)
repaint();
}
// "Drops" the picked balloon, if any.
@Override
public void mouseReleased(MouseEvent e)
{
}
// Not used:
@Override
public void mouseEntered(MouseEvent e)
{
}
@Override
public void mouseExited(MouseEvent e)
{
}
@Override
public void mouseClicked(MouseEvent e)
{
}
}
的{{1}}类。 SquareBalloon()类继承Balloon类。
Balloon有人可以解释为什么在场景＃1 中，DrawingPanel()方法启动后变量int的值的变化没有被传递给public class SquareBalloon extends Balloon implements MouseListener
{
public SquareBalloon()
{
}
/**
* Constructs a balloon with a given center, radius and color
*
* @param x
* x-coordinate of the center
* @param y
* y-coordinate of the center
* @param r
* radius of the balloon
*/
public SquareBalloon(int x, int y, int r)
{
super(x, y, r);
}
/**
* Draws a solid circle if makeItFilled is true and outline only if
* makeItFilled is false
*
* @param g
* graphics context
* @param makeItFilled
* draws a solid circle if true
* @param rotate
* receives rotate variable value set in mousePressed() method of
* DrawingPanel() class
*/
@Override
public void draw(Graphics g, boolean makeItFilled, int rotate)
{
Graphics2D g2d = (Graphics2D) g;
g.setColor(color);
System.out.println("This is the value of rotate" + rotate + "from the draw() method of SquareBalloon() class.");
if (makeItFilled)
{
Rectangle rect2 = new Rectangle(xCenter - radius, yCenter - radius, radius, radius);
if (rotate == 2)
{
System.out.println("This is the value of rotate" + rotate
+ "from the makedItFilled if statement in draw() method of SquareBalloon() class.");
g2d.rotate(45 * (Math.PI / 180));
}
g2d.fill(rect2);
} else
{
Rectangle rect2 = new Rectangle(xCenter - radius, yCenter - radius, radius, radius);
if (rotate == 2)
{
System.out.println("This is the value of rotate" + rotate
+ "from the other if statement in draw() method of SquareBalloon() class.");
g2d.rotate(45 * (Math.PI / 180));
}
g2d.draw(rect2);
}
}
}
的子类class，以便在mousePressed类的Balloon方法中执行条件为 rotate == 2 的if语句？因为在场景＃2 中它确实有用。
谢谢！