java - 绘制用户选择的形状

Question

我需要创建一个程序来绘制形状(用户使用单选按钮选择)，以及是否填充形状(用户使用复选框选择)。这是我到目前为止的代码:

 import javax.swing.*;
 import java.awt.*;
 import java.awt.event.*;

public class SelectShape extends JFrame implements ItemListener{
    private JRadioButton line = new JRadioButton("Line");
    private JRadioButton rect = new JRadioButton("Rectangle");
    private JRadioButton oval = new JRadioButton("Oval");
    private JCheckBox fill = new JCheckBox("Filled");
    private FigurePanel fp;


public static void main(String[] args) {
    SelectShape frame = new SelectShape();
    frame.setTitle("Select Shape");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null);
    frame.setSize(400,400);
    frame.setVisible(true);
}

public SelectShape() {
    JPanel p1 = new JPanel();
    p1.add(fp);
    fp.setBackground(Color.WHITE);
    p1.setSize(200,400);

    JPanel p2 = new JPanel();
    p2.setLayout(new FlowLayout());
    p2.add(line);
    p2.add(rect);
    p2.add(oval);
    p2.add(fill);
    add(p2, "South");

    line.addItemListener(this);
    rect.addItemListener(this);
    oval.addItemListener(this);
    fill.addItemListener(this);

}

public void ItemStateChanged(ItemEvent e) {
    if(rect.isSelected()) {
        FigurePanel.dRect();
        repaint();
    }
    else if(oval.isSelected()) {
        FigurePanel.dOval();
        repaint();
    }
    else if(line.isSelected()) {
        FigurePanel.dLine();
        repaint();
    }
    if(fill.isSelected()) {
        FigurePanel.fill();
        repaint();
    }
    else {
        FigurePanel.erase();
        repaint();
    }
}       
}

class FigurePanel extends JPanel {
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    public void dLine(Graphics g) {
        g.drawLine(10,10,160,10);
    }
    public void dRect(Graphics g) {
        g.drawRect(10,10,150,50);
    }
    public void dOval(Graphics g) {
        g.drawOval(10,10,150,50);
    }

    public void fill(Graphics g) {
        g.setColor(Color.GREEN);
        if(rect.isSelected()) {
            g.fillRect(10,10,150,50);
        }
        else if(oval.isSelected()) {
            g.fillOval(10,10,150,50);
        }
    }
    public void erase(Graphics g) {
        g.setColor(Color.WHITE);
        if(rect.isSelected()) {
            g.fillRect(10,10,150,50);
        }
        else if(oval.isSelected()) {
            g.fillOval(10,10,150,50);
        }
    }
}
}

我收到的错误是预期表达式和标识符的非法开始。如果我应该以另一种方式处理这个问题，请告诉我。

Answer 1

我认为你需要回到基础......

这行不通...

fp.setBackground("white");

Component#setBackground 不采用 String 作为参数，它采用 Color

您的所有 addItemListener 调用都无法正常工作，因为您尚未实现 ItemListener

我不确定您希望通过这样做实现什么......

@Override
fp.dRect();

但这行不通。 @Override 用于指示某个方法被祖先覆盖，您只需调用 FigurePanel

的方法

Java 与 C 和 C++ 一样区分大小写；

没有这样的类itemEvent...它是ItemEvent

public void ItemStateChanged(itemEvent e) {

没有这样的类graphics，它是Graphics

public void paintComponent(graphics g) {

我什至不会尝试猜测您希望通过以下内容实现什么......

public void paintComponent(graphics g) {
    super.paintComponent(g);
    dLine() {
        g.drawLine(10, 10, 160, 10);
    }
    dRect() {
        g.drawRect(10, 10, 150, 50);
    }
    dOval() {
        g.drawOval(10, 10, 150, 50);
    }
    fill() {
        g.setColor(Color.GREEN);
            if (rect.isSelected()) {
                g.fillRect(10, 10, 150, 50);
            } else if (oval.isSelected()) {
                g.fillOval(10, 10, 150, 50);
            }
        }
    erase() {
        g.setColor(Color.WHITE);
        if (rect.isSelected()) {
            g.fillRect(10, 10, 150, 50);
        } else if (oval.isSelected()) {
            g.fillOval(10, 10, 150, 50);
        }
    }
}

Java 不支持“内联方法”(或者您想调用它们的任何名称)，不，使它们成为方法也无法实现您想要做的事情...

事实上，您做得很好的一件事是重写 paintComponent 并调用 super.paintComponent...干得好:D!

已更新

我鼓励您仔细阅读...

• The Java Trails ，尤其是那些涵盖基础知识的内容，尤其是那些涵盖继承的内容
• Custom Painting
• 2D Graphics

更新了可能的运行示例

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Shape;
import java.awt.event.ActionEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.geom.Rectangle2D;
import javax.swing.AbstractAction;
import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class DrawShapes {

    public static void main(String[] args) {
        new DrawShapes();
    }

    public DrawShapes() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                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 {

        public DrawPane() {

            setLayout(new BorderLayout());

            RenderPane rp = new RenderPane();
            add(new ControlsPane(rp), BorderLayout.NORTH);
            add(rp);

        }

    }

    public class ControlsPane extends JPanel {

        public ControlsPane(RenderPane rp) {

            JRadioButton[] btns = new JRadioButton[4];
            btns[0] = new JRadioButton(new LineAction(rp));
            btns[1] = new JRadioButton(new RectangleAction(rp));
            btns[2] = new JRadioButton(new OvalAction(rp));
            btns[3] = new JRadioButton(new ClearAction(rp));

            ButtonGroup bg = new ButtonGroup();
            for (JRadioButton btn : btns) {
                bg.add(btn);
                add(btn);
            }

        }

    }

    public class RenderPane extends JPanel {

        private Shape shape;

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        public void setShape(Shape shape) {
            this.shape = shape;
            repaint();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            if (shape != null) {
                g2d.setColor(Color.RED);
                g2d.draw(shape);
            }
            g2d.dispose();
        }

    }

    public class LineAction extends AbstractRenderAction {

        public LineAction(RenderPane renderPane) {
            super(renderPane);
            putValue(NAME, "Line");
        }

        @Override
        public Shape getShape() {
            return new Line2D.Float(0f, 0f, getRenderPane().getWidth(), getRenderPane().getHeight());
        }

    }

    public class RectangleAction extends AbstractRenderAction {

        public RectangleAction(RenderPane renderPane) {
            super(renderPane);
            putValue(NAME, "Rectangle");
        }

        @Override
        public Shape getShape() {
            return new Rectangle2D.Float(10, 10, getRenderPane().getWidth() - 20, getRenderPane().getHeight() - 20);
        }

    }

    public class OvalAction extends AbstractRenderAction {

        public OvalAction(RenderPane renderPane) {
            super(renderPane);
            putValue(NAME, "Oval");
        }

        @Override
        public Shape getShape() {
            float radius = Math.min(getRenderPane().getWidth() - 20, getRenderPane().getHeight() - 20);
            return new Ellipse2D.Float(10, 10, radius, radius);
        }

    }

    public class ClearAction extends AbstractRenderAction {

        public ClearAction(RenderPane renderPane) {
            super(renderPane);
            putValue(NAME, "Clear");
        }

        @Override
        public Shape getShape() {
            return null;
        }

    }

    public abstract class AbstractRenderAction extends AbstractAction {

        private RenderPane renderPane;

        public AbstractRenderAction(RenderPane renderPane) {
            this.renderPane = renderPane;
        }

        public RenderPane getRenderPane() {
            return renderPane;
        }

        public abstract Shape getShape();

        @Override
        public void actionPerformed(ActionEvent e) {
            getRenderPane().setShape(getShape());
        }

    }

}