我遇到了一个问题，试图从Child Class（Balloon（））中的Parent Class（DrawingPanel（））访问变量（R）的值。
我在DrawingPanel（）的类构造函数中将公共整数R设置为0。像这样：
public class DrawingPanel extends JPanel implements MouseListener,
MouseMotionListener, KeyListener
{
...
public int R;
// Constructor:
public DrawingPanel() {
setBackground(Color.WHITE);
addMouseListener(this);
addMouseMotionListener(this);
addKeyListener(this);
...
R = 0;
}
通过mousePressed（）方法（DrawingPanel（）类的一部分）检测鼠标单击JPanel中的Balloon对象。见下文：
// 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.
public void mousePressed(MouseEvent e) {
...
R = 1;
System.out.print(R);
...
}
在Child Class，Balloon（）中，继承DrawingPanel（）父类，并将R的值打印到控制台。像这样：
/**
* Represents a balloon in the BalloonDraw program.
* Author: Willy Bolly
* Ver 1.0 Created 12/31/17
*/
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import javax.swing.JPanel;
public class Balloon extends DrawingPanel
{
int xCenter, yCenter, radius, rotate = RotateState();
Color color;
/**
* Constructs a balloon with the center at (0, 0),
* radius 50, and blue color
*/
public Balloon()
{
xCenter = 0;
yCenter = 0;
radius = 50;
color = Color.BLUE;
}
/**
* 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
* @param c color of the balloon
*/
public Balloon(int x, int y, int r, Color c)
{
xCenter = x;
yCenter = y;
radius = r;
color = c;
}
/**
* Returns the x-coordinate of the center.
*/
public int getX()
{
System.out.println(rotate);
return xCenter;
}
/**
* Returns the y-coordinate of the center.
*/
public int getY()
{
return yCenter;
}
/**
* Returns the radius of this balloon.
*/
public int getRadius()
{
return radius;
}
/**
* Returns the color of this balloon.
*/
public Color getColor()
{
return color;
}
/**
* Returns the distance from a given point to the
* center of this balloon.
* @param x, y coordinates of the point
*/
public double distance(int x, int y)
{
double dx = x - xCenter;
double dy = y - yCenter;
return Math.sqrt(dx*dx + dy*dy);
}
/**
* Moves the center of this balloon to (x, y)
* @param x x-coordinate of the new center
* @param y y-coordinate of the new center
*/
public void move(int x, int y)
{
xCenter = x;
yCenter = y;
}
/**
* Sets the radius of this balloon to r
* @param r new radius
*/
public void setRadius(int r)
{
radius = r;
}
/**
* Returns true if a given point is strictly inside this balloon;
* otherwise returns false
* @param x, y coordinates of the point
*/
public boolean isInside(int x, int y)
{
return distance(x, y) < 0.9 * radius;
}
/**
* Returns true if a given point is on the border of this balloon;
* otherwise returns false
* @param x, y coordinates of the point
*/
public boolean isOnBorder(int x, int y)
{
double d = distance(x, y);
return d >= 0.9 * radius && d <= 1.1 * radius;
}
//Returns R value from DrawingPanel() class
public int RotateState()
{
return 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
*/
public void draw(Graphics g, boolean makeItFilled)
{
}
}
由于某种原因，Balloon（）类仅获取并输出在DrawingPanel（）类的构造函数中声明的R的值。但是，当mousePressed（）方法启动时，变量R更改后，它无法返回变量R的更新值。
有人可以确定为什么会出现这个问题吗？非常感谢您的反馈。
答案 0 :(得分：0)
在Balloon课程中，您应该覆盖mouseClicked方法并实现其特定于类的逻辑。
所以，将其添加到Balloon类：
@Override
public void mousePressed(MouseEvent e) {
super.mousePressed(e);
// Do stuff with R
getX();
}
答案 1 :(得分：0)
我认为有可能因为继承，Baloon和DrawingPanel的实例被视为单独的，因此有自己的变量和值。 mousePressed方法会将DrawingPanel.R的值更改为1，但不会将Baloon.R的值更改为mousePressed。
覆盖Baloon类中的import re
if re.findall('[\!\$\%\^\&\*\_\-\+\=]', name):
points += 1
方法，如上一个答案中建议的那样，可能会解决您的问题。
答案 2 :(得分：0)
更新＃1
我找到了另一种让程序的旋转功能正常工作的方法。
我将变量R的名称更改为rotate
在DrawingPanel()课程中，我有以下内容：
public class DrawingPanel extends JPanel implements MouseListener, MouseMotionListener, KeyListener {
private ArrayList<Balloon> balloons;
private Balloon activeBalloon;
private Color color;
private DrawingPanel canvas;
private boolean picked, stretching;
private int offsetX, offsetY;
private double offsetR;
int rotate;
// Constructor:
public DrawingPanel() {
setBackground(Color.WHITE);
addMouseListener(this);
addMouseMotionListener(this);
addKeyListener(this);
balloons = new ArrayList<Balloon>();
activeBalloon = null;
picked = false;
stretching = false;
color = Color.BLUE;
rotate = 0;
System.out.println("This is" + rotate + "from the constructor of DrawingPanel()");
}
// 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 RoundBalloon(w / 2, h / 2, radius, color);
break;
case 2:
activeBalloon = new OvalBalloon(w / 2, h / 2, radius, color);
break;
case 3:
activeBalloon = new SquareBalloon(w / 2, h / 2, radius, color);
break;
case 4:
activeBalloon = new FancyBalloon(w / 2, h / 2, radius, color);
break;
default:
activeBalloon = new RoundBalloon(w / 2, h / 2, radius, color);
break;
}
balloons.add(activeBalloon);
repaint();
}
// Repaints this panel. If activeBalloon is set, paints it on top.
public void paintComponent(Graphics g) {
super.paintComponent(g);
for (Balloon b : balloons) {
if (!picked || b != activeBalloon)
{
System.out.println("This is rotate" + rotate + "from paintComponent()");
//Added rotate parameter which takes the rotate value
//from mousePressed() method and passes to the draw()
//object being drawn
b.draw(g, true, rotate);
}
}
if (picked && activeBalloon != null)
//Added rotate parameter which takes the rotate value
//from mousePressed() method and passes to the draw()
//method for the balloon object being drawn
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.
public void mousePressed(MouseEvent e) {
rotate = 1;
System.out.println("This is the value of rotate" + rotate + "from the mousePressed() method in DrawingPanel() class.");
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();
stretching = false;
activeBalloon = b;
} else if (b.isOnBorder(x, y)) {
picked = true;
offsetR = b.distance(x, y) - b.getRadius();
stretching = true;
activeBalloon = b;
}
}
if (picked)
repaint();
}
...
}
在Balloon（）类的子类之一SquareBalloon（）中，我有以下内容：
public class SquareBalloon extends Balloon {
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
* @param c
* color of the balloon
*/
public SquareBalloon(int x, int y, int r, Color c) {
super(x, y, r, c);
}
/**
* 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
*/
public void draw(Graphics g, boolean makeItFilled, int rotate) {
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.WHITE);
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);
//Value from rotate parameter is used for the rotation
if (rotate == 1) {
System.out.println("This is the value of rotate" + rotate
+ "from the makedItFilled if statement in draw() method of SquareBalloon() class.");
g2d.rotate(90);
}
g2d.fill(rect2);
} else {
Rectangle rect2 = new Rectangle(xCenter - radius, yCenter - radius, radius, radius);
//Value from rotate parameter is used for the rotation
if (rotate == 1) {
System.out.println("This is the value of rotate" + rotate
+ "from the other if statement in draw() method of SquareBalloon() class.");
g2d.rotate(90);
}
g2d.draw(rect2);
}
}
}
旋转很好。但现在的麻烦是我无法弄清楚如何重置rotate参数的值，以便在创建新对象时不会发生旋转。
在我的代码的当前格式中，该参数仅考虑在rotate方法上设置的变量mousePressed()的值。
有人可以建议我应该做什么，以便旋转参数考虑到变量rotate的值的变化，而不是mousePressed()方法吗？
答案 3 :(得分：0)
更新＃2
我修复了上一篇文章（更新＃1）中描述的问题。
DrawingPanel()类如下所示：
public class DrawingPanel extends JPanel implements MouseListener, MouseMotionListener, KeyListener {
private ArrayList<Balloon> balloons;
private Balloon activeBalloon;
private Color color;
private DrawingPanel canvas;
private boolean picked, stretching;
private int offsetX, offsetY;
private double offsetR;
int rotate;
// Constructor:
public DrawingPanel() {
setBackground(Color.WHITE);
addMouseListener(this);
addMouseMotionListener(this);
addKeyListener(this);
balloons = new ArrayList<Balloon>();
activeBalloon = null;
picked = false;
stretching = false;
color = Color.BLUE;
rotate = 0;
System.out.println("This is" + rotate + "from the constructor of DrawingPanel()");
}
// Called from controlPanel when the "Pick color" button is clicked.
public void pickColor() {
Color pickedColor = JColorChooser.showDialog(this, "Pick a color", color);
if (pickedColor != null)
color = pickedColor;
}
// Returns the current color.
public Color getColor() {
return color;
}
// 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 RoundBalloon(w / 2, h / 2, radius, color);
break;
case 2:
activeBalloon = new OvalBalloon(w / 2, h / 2, radius, color);
break;
case 3:
activeBalloon = new SquareBalloon(w / 2, h / 2, radius, color);
break;
case 4:
activeBalloon = new FancyBalloon(w / 2, h / 2, radius, color);
break;
default:
activeBalloon = new RoundBalloon(w / 2, h / 2, radius, color);
break;
}
balloons.add(activeBalloon);
repaint();
}
// Repaints this panel. If activeBalloon is set, paints it on top.
public void paintComponent(Graphics g) {
super.paintComponent(g);
for (Balloon b : balloons) {
if (!picked || b != activeBalloon)
{
//Added this check to restore original angle of balloon
//objects.
if(rotate > 1)
rotate = 0;
System.out.println("This is rotate" + rotate + "from paintComponent()");
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.
public void mousePressed(MouseEvent e) {
//Value for parameter rotate is set here on mouse click
//Changed the counter so its value is not set to 1
//but it would add up.
rotate++;
System.out.println("This is the value of rotate" + rotate + "from the mousePressed() method in DrawingPanel() class.");
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();
stretching = false;
activeBalloon = b;
} else if (b.isOnBorder(x, y)) {
picked = true;
offsetR = b.distance(x, y) - b.getRadius();
stretching = true;
activeBalloon = b;
}
}
if (picked)
repaint();
}
...
}
在Balloon（）类的子类之一SquareBalloon（）中，我有以下内容：
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
* @param c
* color of the balloon
*/
public SquareBalloon(int x, int y, int r, Color c) {
super(x, y, r, c);
}
/**
* 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
*/
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 == 1) {
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 == 1) {
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);
}
}
}