Java 为什么'；当我单击时，圆圈是否出现？
我必须使用HoltSoft的Ready to Program中的Console类。我不应该使用swing，所以如果没有swing我做不到，请忽略这个Java 为什么'；当我单击时，圆圈是否出现？,java,swing,graphics,mouseevent,Java,Swing,Graphics,Mouseevent,我必须使用HoltSoft的Ready to Program中的Console类。我不应该使用swing，所以如果没有swing我做不到，请忽略这个 //imports import java.awt.*; import java.awt.event.*; import hsa.*; public class DrawLines extends Panel implements MouseListener, MouseMotionListener { Console c; i
//imports
import java.awt.*;
import java.awt.event.*;
import hsa.*;
public class DrawLines extends Panel implements MouseListener, MouseMotionListener
{
Console c;
int startX, startY, prevX, prevY; //mouse coordinates
private boolean dragging; //whether or not the mouse is being dragged
MouseEvent e;
public DrawLines ()
{
c = new Console (); //creates console window
addMouseListener (this); //detects press/release
addMouseMotionListener (this);//detects dragging
}
public void mousePressed (MouseEvent e)
{
while (!dragging)
{
try
{
startX = e.getX ();//get the
startY = e.getY ();//original co-ordinates
dragging = true;
}
catch (NullPointerException q) //because I kept getting this error
{
}
}
}
public void mouseDragged (MouseEvent e)
{
while (dragging)
{
try
{
int x = e.getX (); //gets and
int y = e.getY (); //updates
prevX = x; //the mouse
prevY = y; //coordinates
}
catch (NullPointerException q)//because I kept getting this error
{
}
}
}
public void mouseReleased (MouseEvent e)
{
dragging = false; //stopped dragging
}
public void drawTheLine ()
{
mousePressed (e);
mouseDragged (e);
c.setColor (Color.black);
c.fillOval (prevX, prevY, 50, 50); //draws a circle where the mouse is
mouseReleased (e);
}
public void mouseMoved (MouseEvent e){}
public void mouseEntered (MouseEvent e){}
public void mouseExited (MouseEvent e){}
public void mouseClicked (MouseEvent e){}
public static void main (String[] args)
{
DrawLines a = new DrawLines ();
a.drawTheLine ();
}
}
public void drawTheLine ()
{
while (true)
{
mousePressed (e);
mouseDragged (e);
c.setColor (Color.black);
c.fillOval (prevX, prevY, 50, 50); //draws a circle where the mouse is
mouseReleased (e);
}
}
public class DrawLines extends Panel
implements MouseListener, MouseMotionListener
{
MouseEvent e; // IT IS NEVER SET TO ANYTHING! IT IS NULL!!!
e = (something);
public void drawTheLine ()
{
while (true)
{
mousePressed (e);
mouseDragged (e);
c.setColor (Color.black);
c.fillOval (prevX, prevY, 50, 50); //draws a circle where the mouse is
mouseReleased (e);
}
}
public class DrawLines extends Panel
implements MouseListener, MouseMotionListener
{
MouseEvent e; // IT IS NEVER SET TO ANYTHING! IT IS NULL!!!
e = (something);
Swing是一个事件驱动系统，是一个单线程系统 这意味着您的应用程序“等待”事件发生（由事件调度线程负责），任何阻止EDT（如循环、长时间运行的进程或阻止IO）的人都会阻止您的应用程序接收这些事件的通知，从而使您的应用程序无法运行 所以，如果我们看看这个
while (true)
{
mousePressed (e);
mouseDragged (e);
c.setColor (Color.black);
c.fillOval (prevX, prevY, 50, 50);
mouseReleased (e);
}
}
drawLineMethodpublic static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception ex) {
}
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new DrawLines());
// I prefer pack, but you've not specified a preferred size for your panel...
//frame.pack();
frame.setSize(400, 400);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
控制台类是什么，但在鼠标事件方法中，您需要更新它，以便它可以更新其输出
用示例更新
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception ex) {
}
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new DrawPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class DrawPane extends JPanel {
private Point center;
private int radius;
public DrawPane() {
MouseAdapter handler = new MouseAdapter() {
@Override
public void mousePressed(MouseEvent e) {
center = e.getPoint();
radius = 0;
repaint();
}
@Override
public void mouseDragged(MouseEvent e) {
int width = Math.max(e.getX(), center.x) - Math.min(e.getX(), center.x);
int height = Math.max(e.getY(), center.y) - Math.min(e.getY(), center.y);
radius = Math.max(width, height);
repaint();
}
};
addMouseListener(handler);
addMouseMotionListener(handler);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (center != null) {
g.setColor(Color.RED);
g.fillOval(center.x - 2, center.y - 2, 4, 4);
g.drawOval(center.x - (radius / 2), center.y - (radius / 2), radius, radius);
}
}
}
}
我建议你花点时间通读一下
- 了解Swing的整体基础知识
- 了解如何在Swing中实际执行自定义绘制
- 由于所有希望在Swing中执行自定义绘制的开发人员都需要了解它是如何工作的
使用纯AWT版本更新
正如有人向我指出的，OP使用AWT而不是Swing，为什么，因为他们似乎能够
public class DrawCircleAWT {
public static void main(String[] args) {
new DrawCircleAWT();
}
public DrawCircleAWT() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
Frame frame = new Frame("Testing");
frame.addWindowListener(new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
frame.setLayout(new BorderLayout());
frame.add(new DrawPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class DrawPane extends Panel {
private Point center;
private int radius;
public DrawPane() {
MouseAdapter handler = new MouseAdapter() {
@Override
public void mousePressed(MouseEvent e) {
center = e.getPoint();
radius = 0;
repaint();
}
@Override
public void mouseDragged(MouseEvent e) {
int width = Math.max(e.getX(), center.x) - Math.min(e.getX(), center.x);
int height = Math.max(e.getY(), center.y) - Math.min(e.getY(), center.y);
radius = Math.max(width, height);
repaint();
}
};
addMouseListener(handler);
addMouseMotionListener(handler);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
@Override
public void paint(Graphics g) {
super.paint(g);
if (center != null) {
g.setColor(Color.RED);
g.fillOval(center.x - 2, center.y - 2, 4, 4);
g.drawOval(center.x - (radius / 2), center.y - (radius / 2), radius, radius);
}
}
}
}
Swing是一个事件驱动系统，是一个单线程系统
这意味着您的应用程序“等待”事件发生（由事件调度线程负责），任何阻止EDT（如循环、长时间运行的进程或阻止IO）的人都会阻止您的应用程序接收这些事件的通知，从而使您的应用程序无法运行
所以，如果我们看看这个
while (true)
{
mousePressed (e);
mouseDragged (e);
c.setColor (Color.black);
c.fillOval (prevX, prevY, 50, 50);
mouseReleased (e);
}
}
这表明……第一，你不了解Swing中事件是如何生成的；第二，EDT实际上是如何工作的
与某些UI框架不同，您不需要实现事件循环，这由Swing负责。这样阻塞EDT将阻止它处理事件
取而代之的是，删除drawLineMethod
，因为它对您毫无帮助，而将您的main方法替换为
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception ex) {
}
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new DrawLines());
// I prefer pack, but you've not specified a preferred size for your panel...
//frame.pack();
frame.setSize(400, 400);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
现在。我不知道控制台类是什么，但在鼠标事件方法中，您需要更新它，以便它可以更新其输出
用示例更新
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception ex) {
}
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new DrawPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class DrawPane extends JPanel {
private Point center;
private int radius;
public DrawPane() {
MouseAdapter handler = new MouseAdapter() {
@Override
public void mousePressed(MouseEvent e) {
center = e.getPoint();
radius = 0;
repaint();
}
@Override
public void mouseDragged(MouseEvent e) {
int width = Math.max(e.getX(), center.x) - Math.min(e.getX(), center.x);
int height = Math.max(e.getY(), center.y) - Math.min(e.getY(), center.y);
radius = Math.max(width, height);
repaint();
}
};
addMouseListener(handler);
addMouseMotionListener(handler);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (center != null) {
g.setColor(Color.RED);
g.fillOval(center.x - 2, center.y - 2, 4, 4);
g.drawOval(center.x - (radius / 2), center.y - (radius / 2), radius, radius);
}
}
}
}
我建议你花点时间通读一下
- 了解Swing的整体基础知识
- 了解如何在Swing中实际执行自定义绘制
- 由于所有希望在Swing中执行自定义绘制的开发人员都需要了解它是如何工作的
使用纯AWT版本更新
正如有人向我指出的，OP使用AWT而不是Swing，为什么，因为他们似乎能够
public class DrawCircleAWT {
public static void main(String[] args) {
new DrawCircleAWT();
}
public DrawCircleAWT() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
Frame frame = new Frame("Testing");
frame.addWindowListener(new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
frame.setLayout(new BorderLayout());
frame.add(new DrawPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class DrawPane extends Panel {
private Point center;
private int radius;
public DrawPane() {
MouseAdapter handler = new MouseAdapter() {
@Override
public void mousePressed(MouseEvent e) {
center = e.getPoint();
radius = 0;
repaint();
}
@Override
public void mouseDragged(MouseEvent e) {
int width = Math.max(e.getX(), center.x) - Math.min(e.getX(), center.x);
int height = Math.max(e.getY(), center.y) - Math.min(e.getY(), center.y);
radius = Math.max(width, height);
repaint();
}
};
addMouseListener(handler);
addMouseMotionListener(handler);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
@Override
public void paint(Graphics g) {
super.paint(g);
if (center != null) {
g.setColor(Color.RED);
g.fillOval(center.x - 2, center.y - 2, 4, 4);
g.drawOval(center.x - (radius / 2), center.y - (radius / 2), radius, radius);
}
}
}
}
当你得到一个异常时，通常意味着出了问题。仅仅忽略它（使用空的catch语句）并不能解决根本的问题？您应该使用JPanel
并覆盖paintComponent
我觉得使用while循环是非常危险的。。。这个程序完成了吗？在我看来，它有很多无限期挂起的可能性，比如mouseDragged（…）为什么要在这个千年中使用AWT组件？@Andrew Thompson我不得不，学校项目。当你遇到异常时，通常意味着出了问题。仅仅忽略它（使用空的catch语句）并不能解决根本的问题？您应该使用JPanel
并覆盖paintComponent
我觉得使用while循环是非常危险的。。。这个程序完成了吗？在我看来，它有很多无限期悬挂的可能性，比如mouseDragged（…）为什么要在这个千年中使用AWT组件？@Andrew Thompson我必须，学校项目。我可以设置它什么？MouseEvent变量有值吗？@helpmeimdumb您根本不应该使用MouseEvent对象。从我所看到的，它看起来像一个java.awt.Point2D适合你的需要。。。那是什么意思？考虑到他们已经这样做了，这可能意味着他们不知道在构造函数中的某些地方应该这样做，这样它就不再是空的：你在开玩笑吧。@MadProgrammer很有趣，你批评我说“看这个”，然后我给他看了部分代码。你真的做了完全一样的事情：（引用你自己的答案）“那么，如果我们看一下这个…”（同一段代码）。我能把它设置成什么？