编辑：我想出来并完成了程序（最后）。谢谢大家的帮助！
我正在尝试创建一个简单的绘图程序，用户可以单击单选按钮选择可以通过拖动鼠标在面板上绘制的形状。我只是想让代码执行此操作，因为我想自己想出来并认为我可以。但是我在行上声明了方法“public void newShape（String shape）{”。我在这一行上得到了4个错误。其中两个是“错误：非法开始表达”，另外两个是“错误：';'预期”。如果有人可以帮助我并告诉我我做错了什么，我会非常感激。
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.event.*;
public class HW4_Paint extends JFrame {
private static Color color = Color.BLACK; // current selected drawing color
private static boolean filled = false; // fill mode - "Filled" or "Empty"
private static String currentShape = "Line"; // current selected shape
private static ArrayList<Shape> shapes = new ArrayList<Shape>(); // a list of all of the shapes in the current drawing
public static void main(String[] args) {
// create the frame and format it
JFrame frame = new HW4_Paint();
frame.setTitle("Paint Program");
frame.setSize(800,500);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public HW4_Paint() {
// create the menu bar
JMenuBar jmb = new JMenuBar();
setJMenuBar(jmb);
// make the file menu
JMenu fileMenu = new JMenu("File");
fileMenu.setMnemonic('F');
jmb.add(fileMenu);
// make the exit menu item under the file menu
JMenuItem exitMenuItem = new JMenuItem("Exit", 'X');
fileMenu.add(exitMenuItem);
exitMenuItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.exit(0);
}
});
// make the help menu
JMenu helpMenu = new JMenu("Help");
helpMenu.setMnemonic('H');
jmb.add(helpMenu);
// make the help menu item under the help menu
JMenuItem helpMenuItem = new JMenuItem("Help", 'H');
helpMenu.add(helpMenuItem);
helpMenuItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
String message = "This program allows you to draw pictures using different shapes and colors.\n"
+ "To change what shape you are drawing with, select the button next to Line, Oval, or Rectangle, depending on which shape you want to draw with.\n"
+ "If you want the shape to be filled in (only applicable with oval and rectangle), select the checkbox next to Filled.\n"
+ "To change the color of the shape that you are drawing, click the button of the color that you want to change to.\n"
+ "To undo the last shape that you drew, click the undo button once. You can repeat this as many times as you want until there are no remaining shapes.\n"
+ "To clear all of the shapes that you have drawn, click the Clear All button.";
JOptionPane.showMessageDialog(null, message, "Help", JOptionPane.INFORMATION_MESSAGE);
}
});
// make the about menu item under the help menu
JMenuItem aboutMenuItem = new JMenuItem("About", 'A');
helpMenu.add(aboutMenuItem);
aboutMenuItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
String message = "HW4_Paint Program\n\n" + "Written by Joey Drees\n\n" + "CSC 360-001";
JOptionPane.showMessageDialog(null, message, "About", JOptionPane.INFORMATION_MESSAGE);
}
});
// make the panels that will be added to the frame for the GUI
JPanel guiPanel = new JPanel();
guiPanel.setLayout(new BorderLayout());
JPanel colorPanel = new JPanel(new FlowLayout());
JPanel buttonPanel = new JPanel(new GridLayout(6,1));
JPanel drawingPanel = new DrawingPanel();
// add the guiPanel to the frame and them add the other panels to the guiPanel
add(guiPanel);
guiPanel.add(colorPanel, BorderLayout.SOUTH);
guiPanel.add(buttonPanel, BorderLayout.EAST);
guiPanel.add(drawingPanel, BorderLayout.CENTER);
// create and add the buttons that will allow the user to change the color of the shapes
JButton blackButton = new JButton("Black");
colorPanel.add(blackButton);
blackButton.setSelected(true);
JButton whiteButton = new JButton("White");
colorPanel.add(whiteButton);
JButton grayButton = new JButton("Gray");
colorPanel.add(grayButton);
JButton redButton = new JButton("Red");
colorPanel.add(redButton);
JButton yellowButton = new JButton("Yellow");
colorPanel.add(yellowButton);
JButton greenButton = new JButton("Green");
colorPanel.add(greenButton);
JButton blueButton = new JButton("Blue");
colorPanel.add(blueButton);
JButton newColorButton = new JButton("New Color");
colorPanel.add(newColorButton);
// create and add the radio buttons to a button group that will allow the user to change the shape they are drawing with
ButtonGroup jbtGroup = new ButtonGroup();
JRadioButton jrbLine = new JRadioButton("Line");
jrbLine.setMnemonic('L');
jbtGroup.add(jrbLine);
buttonPanel.add(jrbLine);
jrbLine.setSelected(true);
jrbLine.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent E) {
currentShape = "Line";
guiPanel.newShape(currentShape);
repaint();
}
});
JRadioButton jrbOval = new JRadioButton("Oval");
jrbOval.setMnemonic('O');
jbtGroup.add(jrbOval);
buttonPanel.add(jrbOval);
jrbOval.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent E) {
currentShape = "Oval";
guiPanel.newShape(currentShape);
repaint();
}
});
JRadioButton jrbRectangle = new JRadioButton("Rectangle");
jrbRectangle.setMnemonic('R');
jbtGroup.add(jrbRectangle);
buttonPanel.add(jrbRectangle);
jrbLine.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent E) {
currentShape = "Rectangle";
guiPanel.newShape(currentShape);
repaint();
}
});
// create and add the check box that will allow the user to create filled shapes
JCheckBox jcbFilled = new JCheckBox("Filled");
jcbFilled.setMnemonic('F');
buttonPanel.add(jcbFilled);
if (jrbLine.isSelected())
jcbFilled.setEnabled(false);
else
jcbFilled.setEnabled(true);
// create and add the buttons that will allow the user to undo their last shape and clear the whole panel
JButton undoButton = new JButton("Undo");
undoButton.setMnemonic('U');
buttonPanel.add(undoButton);
JButton clearAllButton = new JButton("Clear All");
clearAllButton.setMnemonic('C');
buttonPanel.add(clearAllButton);
// create the action listener for the undo button
undoButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!shapes.isEmpty()) {
shapes.remove(shapes.size() - 1);
repaint();
}
}
});
// create the action listener for the clear all button
clearAllButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!shapes.isEmpty()) {
shapes.clear();
repaint();
}
}
});
public void newShape(String shape) {
switch (shape) {
case "Line":
Shape line = new Line(startX, startY, endX, endY);
shapes.add(line);
break;
case "Oval":
Shape oval = new Oval(startX, startY, endX, endY);
shapes.add(oval);
break;
case "Rectangle":
Shape rectangle = new Rectangle(startX, startY, endX, endY);
shapes.add(rectangle);
break;
default:
System.out.println("ERROR. Check logic.");
}
}
}
}
private class DrawingPanel extends JPanel {
private int startX, startY, endX, endY;
public DrawingPanel() { // sets the background to white and adds the required listeners
setBackground(Color.WHITE);
addMouseListener(new MouseAdapter() {
public void mousePressed(MouseEvent e) {
startX = endX = e.getX();
startY = endY = e.getY();
}
});
addMouseMotionListener(new MouseMotionAdapter() {
@Override
public void mouseDragged(MouseEvent e) {
endX = e.getX();
endY = e.getY();
Shape lastShape = shapes.get(shapes.size()-1);
lastShape.setEnd(endX, endY);
repaint();
}
});
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
for (Shape shape: shapes)
shape.draw(g);
}
}
答案 0 :(得分：1)
有两个额外的花括号
}
}
删除这两个
您需要在构造函数}中保留一个HW4_Paint()，并从方法}中删除一个newShape(String shape)
答案 1 :(得分：1)
} // ADD IT HERE
public void newShape(String shape) {
switch (shape) {
case "Line":
Shape line = new Line(startX, startY, endX, endY);
shapes.add(line);
break;
case "Oval":
Shape oval = new Oval(startX, startY, endX, endY);
shapes.add(oval);
break;
case "Rectangle":
Shape rectangle = new Rectangle(startX, startY, endX, endY);
shapes.add(rectangle);
break;
default:
System.out.println("ERROR. Check logic.");
}
}
} // REMOVE IT FROM HERE
}
答案 2 :(得分：1)
您似乎在newShape类的构造函数中声明了HW4_Paint方法。
在}之前添加public void newShape(String shape) {，并在该方法后删除一个}。
看起来应该更像......
// create the action listener for the clear all button
clearAllButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!shapes.isEmpty()) {
shapes.clear();
repaint();
}
}
});
} // Add me
public void newShape(String shape) {
switch (shape) {
case "Line":
Shape line = new Line(startX, startY, endX, endY);
shapes.add(line);
break;
case "Oval":
Shape oval = new Oval(startX, startY, endX, endY);
shapes.add(oval);
break;
case "Rectangle":
Shape rectangle = new Rectangle(startX, startY, endX, endY);
shapes.add(rectangle);
break;
default:
System.out.println("ERROR. Check logic.");
}
}
// Remove a } from here, so you should end with these 3, not 4
}
答案 3 :(得分：0)
欢迎使用StackOverflow！我赞赏你想要自己解决问题的愿望，所以我不会只给你答案。
您收到该消息是因为newShape()位置错误。也许它的范围太远了？也许它太过分了？检查程序在IDE中的缩进 - 它在哪里？你期望它在那里吗？
答案 4 :(得分：0)
据我所知，错误如＆＃34;非法开始表达＆＃34;或＆＃34;＆＃39;;＆＃39;预期＆＃34;通常意味着你对{}做错了。我有38个与实际代码行完全无关的错误，但都是由于遗忘而导致的。