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在Liang的第15章Intro to Java Programming（第7版）中，他介紹了一個程序來創建一個（2D）球一個JPanel並通過點擊放大/縮小按鈕將其放大。我已經修改了程序，以便它還可以1）當用戶點擊/選項+點擊時放大/縮小球，2）允許您通過按下按鈕選擇球的顏色，3）允許您移動球用鼠標拖動它可以圈選。有沒有更好的方法來設置JPanel圖形的初始位置？）
最後一次修改是我給了我一段時間的麻煩，因爲我想在開始時將球居中，但是隨後允許用戶用鼠標移動球。我想出的解決方案是讓paintComponent方法只在第一次繪製時將球的x座標和y座標設置爲getWidth（）和getHeight（）。爲此，我在BallCanvas類中添加了一個paintCount變量，並創建了一個if語句，以便它僅在第一次執行時執行。當我試圖找出最初如何做到這一點時，我看到了其他解決方案，例如：Why can't I access my panel's getWidth() and getHeight() functions?，但我發現我的解決方案更簡單。
所以問題是：我認爲是否認爲不好的編碼風格？專業程序員會嘲笑這個解決方案嗎？還是可以嗎？
更重要的是，有沒有更好的（而且也比較簡單）的方法來做到這一點，不涉及設立櫃臺？
下面是代碼中的相關位：
BallCanvas的開始：
public static class BallCanvas extends JPanel {
private int radius = 20;
private Color color = Color.BLACK;
private int ballX;
private int ballY;
private int paintCount = 0;
...
此舉方法（這是爲了響應一個的mouseDragged事件）：
public void move(MouseEvent e){
ballX = e.getX() - radius;
ballY = e.getY() - radius;
repaint();
}
的的paintComponent方法：
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(color);
if(paintCount < 1){
ballX = getWidth()/2 - radius;
ballY = getHeight()/2 - radius;
}
g.fillOval(ballX, ballY, 2*radius, 2*radius);
paintCount++;
}
全部程序：
// Reference: Liang's Intro to Java Programming
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class ControlBall extends JFrame{
private JButton jbtRed = new JButton("Red");
private JButton jbtGreen = new JButton("Green");
private JButton jbtBlue = new JButton("Blue");
private JButton jbtBlack = new JButton("Black");
private BallCanvas canvas = new BallCanvas();
private JMenuBar menuBar = new JMenuBar();
private JMenu menu = new JMenu("Edit");
private JMenuItem miEnlarge = new JMenuItem("Enlarge");
private JMenuItem miShrink = new JMenuItem("Shrink");
public ControlBall(){
menuBar.add(menu);
menu.add(miEnlarge);
menu.add(miShrink);
JPanel panel = new JPanel();
panel.add(jbtRed);
panel.add(jbtGreen);
panel.add(jbtBlue);
panel.add(jbtBlack);
this.add(canvas, BorderLayout.CENTER);
this.add(panel, BorderLayout.SOUTH);
this.add(menuBar, BorderLayout.NORTH);
jbtRed.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){
canvas.setColor(Color.RED);
}
});
jbtGreen.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){
canvas.setColor(Color.GREEN);
}
});
jbtBlue.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){
canvas.setColor(Color.BLUE);
}
});
jbtBlack.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){
canvas.setColor(Color.BLACK);
}
});
miEnlarge.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){
canvas.enlarge();
}
});
miShrink.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){
canvas.shrink();
}
});
canvas.addMouseListener(new MouseListener() {
public void mouseClicked(MouseEvent e){
canvas.changeSize(e);
}
public void mousePressed(MouseEvent e){}
public void mouseReleased(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
public void mouseExited(MouseEvent e){}
});
canvas.addMouseMotionListener(new MouseMotionAdapter() {
public void mouseDragged(MouseEvent e) {
canvas.move(e);
}
});
}
public static void main(String[] args){
JFrame frame = new ControlBall();
frame.setTitle("ControlBall");
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 200);
frame.setVisible(true);
}
public static class BallCanvas extends JPanel {
private int radius = 20;
private Color color = Color.BLACK;
private int ballX;
private int ballY;
private int paintCount = 0;
public BallCanvas(){
System.out.println(getWidth() + " " + getHeight());
}
public BallCanvas(int initialRadius){
radius = initialRadius;
}
public void setColor(Color color){
this.color = color;
repaint();
}
public void changeSize(MouseEvent e){
int numClicks = e.getClickCount();
if(e.isAltDown()){
if(radius >= 6){
this.radius -= 5*numClicks;
} else{
// do nothing
}
} else{
this.radius += 5*numClicks;
}
repaint();
}
public void enlarge(){
this.radius += 5;
repaint();
}
public void shrink(){
if(radius >= 10){
this.radius -= 5;
}
repaint();
}
public void move(MouseEvent e){
ballX = e.getX() - radius;
ballY = e.getY() - radius;
repaint();
}
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(color);
if(paintCount < 1){
ballX = getWidth()/2 - radius;
ballY = getHeight()/2 - radius;
}
g.fillOval(ballX, ballY, 2*radius, 2*radius);
paintCount++;
}
}
}
我不認爲這是不好的編程風格。但是，再次，我不是一個專業人士。這個問題可能會引出基於意見的，而不是基於事實的答案，所以我正在投票結束。 – Jeffrey
也許如果我將焦點改爲「是否有更好的方法可以做到這一點？」這會是一個更合適的問題嗎？ –
+1 [sscce]（http://sscce.org/） – trashgod