有关Java画图，求教！

Question

Frame不支持main方法的,你可以在Frame内部添加一个支持paint方法的控件,如Panel等等.

Answer 1

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Label;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.ArrayList;import javax.swing.SwingUtilities;public class DrawLine extends Frame
{    public static void main(String[] args)
    {
        DrawLine frame = new DrawLine();
        Dimension dmnScreen = Toolkit.getDefaultToolkit().getScreenSize();
        Dimension dmnMain = new Dimension(650, 550);        frame.setTitle("画图测试");
        frame.setSize(dmnMain);
        frame.setLocation(
            (dmnScreen.width - dmnMain.width) / 2,
            (dmnScreen.height - dmnMain.height) / 2);
        frame.setVisible(true);
    }
    private ArrayList altPtDown = new ArrayList();
    private ArrayList altPtUp = new ArrayList();
    private Graphics2D big;
    private Label lblStatus = new Label();
    private Point ptDown;
    private Point ptMove;
    private Point ptMoveOld;
    private String strStatus;    DrawLine()
    {
        super ();
        init();
    }    private void init()
    {
        add(lblStatus, BorderLayout.SOUTH);
        addWindowListener(new WindowAdapter()
        {
            public void windowClosing(WindowEvent arg0)
            {
                System.exit(0);
            }
        });        this.addMouseMotionListener(new MouseMotionListener()
        {
            public void mouseDragged(MouseEvent arg0)
            {
                if (SwingUtilities.isLeftMouseButton(arg0))
                {
                    ptMove = arg0.getPoint();
                    repaint();
                }
            }            public void mouseMoved(MouseEvent arg0)
            {            }
        });        this.addMouseListener(new MouseListener()
        {
            public void mouseClicked(MouseEvent arg0)
            {            }            public void mouseEntered(MouseEvent arg0)
            {            }            public void mouseExited(MouseEvent arg0)
            {            }            public void mousePressed(MouseEvent arg0)
            {
                ptDown = new Point(arg0.getPoint());
                ptMove = new Point(ptDown);
                ptMoveOld = new Point(ptDown);
                altPtDown.add(ptDown);
            }            public void mouseReleased(MouseEvent arg0)
            {
                ptMove = new Point(arg0.getPoint());
                altPtUp.add(ptMove);
                ptDown = null;
                ptMove = null;
                ptMoveOld = null;
            }
        });
    }    //当窗口被遮住,再显示的时候,调用此方法重绘
    public void paint(Graphics g)
    {
        super.paint(g);
        big = (Graphics2D) g;
        g.setColor(Color.BLACK);        for (int i = 0; i < altPtDown.size(); i++)
        {
            ptDown = (Point) altPtDown.get(i);
            ptMove = (Point) altPtUp.get(i);
            if (ptMove.x > ptDown.x)
            {
                if (ptMove.y > ptDown.y)
                {
                    g.drawRect(
                        ptDown.x,
                        ptDown.y,
                        ptMove.x - ptDown.x,
                        ptMove.y - ptDown.y);
                    g.drawOval(
                        ptDown.x,
                        ptDown.y,
                        ptMove.x - ptDown.x,
                        ptMove.y - ptDown.y);
                }
                else
                {
                    g.drawRect(
                        ptDown.x,
                        ptMove.y,
                        ptMove.x - ptDown.x,
                        ptDown.y - ptMove.y);
                    g.drawOval(
                        ptDown.x,
                        ptMove.y,
                        ptMove.x - ptDown.x,
                        ptDown.y - ptMove.y);
                }
            }
            else
            {
                if (ptMove.y > ptDown.y)
                {
                    g.drawRect(
                        ptMove.x,
                        ptDown.y,
                        ptDown.x - ptMove.x,
                        ptMove.y - ptDown.y);
                    g.drawOval(
                        ptMove.x,
                        ptDown.y,
                        ptDown.x - ptMove.x,
                        ptMove.y - ptDown.y);
                }
                else
                {
                    g.drawRect(
                        ptMove.x,
                        ptMove.y,
                        ptDown.x - ptMove.x,
                        ptDown.y - ptMove.y);
                    g.drawOval(
                        ptMove.x,
                        ptMove.y,
                        ptDown.x - ptMove.x,
                        ptDown.y - ptMove.y);
                }
            }
        }
    }

Answer 2

private void swapPoint(Point aPt, Point aPts)
    {
        int intTmp;        if (aPt.x > aPts.x)
        {
            intTmp = aPt.x;
            aPt.x = aPts.x;
            aPts.x = intTmp;
        }        if (aPt.y > aPts.y)
        {
            intTmp = aPt.y;
            aPt.y = aPts.y;
            aPts.y = intTmp;
        }
    }    /* (non-Javadoc)
     * @see java.awt.Component#update(java.awt.Graphics)
     */
    //当画图时调用此方法重绘
    public void update(Graphics g)
    {
        super.paint(g);
        big = (Graphics2D) g;        if (ptDown == null)
            return;
        if (ptMove == null)
            return;
        if (ptMoveOld == null)
            return;
        //Erase Old ======================
        g.setColor(getBackground());
        g.drawLine(ptDown.x, ptDown.y, ptMoveOld.x, ptMoveOld.y);
        if (ptMoveOld.x > ptDown.x)
        {
            if (ptMoveOld.y > ptDown.y)
            {
                g.drawRect(
                    ptDown.x,
                    ptDown.y,
                    ptMoveOld.x - ptDown.x,
                    ptMoveOld.y - ptDown.y);
                g.drawOval(
                    ptDown.x,
                    ptDown.y,
                    ptMoveOld.x - ptDown.x,
                    ptMoveOld.y - ptDown.y);
            }
            else
            {
                g.drawRect(
                    ptDown.x,
                    ptMoveOld.y,
                    ptMoveOld.x - ptDown.x,
                    ptDown.y - ptMoveOld.y);
                g.drawOval(
                    ptDown.x,
                    ptMoveOld.y,
                    ptMoveOld.x - ptDown.x,
                    ptDown.y - ptMoveOld.y);
            }
        }
        else
        {
            if (ptMoveOld.y > ptDown.y)
            {
                g.drawRect(
                    ptMoveOld.x,
                    ptDown.y,
                    ptDown.x - ptMoveOld.x,
                    ptMoveOld.y - ptDown.y);
                g.drawOval(
                    ptMoveOld.x,
                    ptDown.y,
                    ptDown.x - ptMoveOld.x,
                    ptMoveOld.y - ptDown.y);
            }
            else
            {
                g.drawRect(
                    ptMoveOld.x,
                    ptMoveOld.y,
                    ptDown.x - ptMoveOld.x,
                    ptDown.y - ptMoveOld.y);
                g.drawOval(
                    ptMoveOld.x,
                    ptMoveOld.y,
                    ptDown.x - ptMoveOld.x,
                    ptDown.y - ptMoveOld.y);
            }
        }        //Draw New ======================
        g.setColor(Color.BLACK);
        g.drawLine(ptDown.x, ptDown.y, ptMove.x, ptMove.y);
        if (ptMove.x > ptDown.x)
        {
            if (ptMove.y > ptDown.y)
            {
                g.drawRect(
                    ptDown.x,
                    ptDown.y,
                    ptMove.x - ptDown.x,
                    ptMove.y - ptDown.y);
                g.drawOval(
                    ptDown.x,
                    ptDown.y,
                    ptMove.x - ptDown.x,
                    ptMove.y - ptDown.y);
            }
            else
            {
                g.drawRect(
                    ptDown.x,
                    ptMove.y,
                    ptMove.x - ptDown.x,
                    ptDown.y - ptMove.y);
                g.drawOval(
                    ptDown.x,
                    ptMove.y,
                    ptMove.x - ptDown.x,
                    ptDown.y - ptMove.y);
            }
        }
        else
        {
            if (ptMove.y > ptDown.y)
            {
                g.drawRect(
                    ptMove.x,
                    ptDown.y,
                    ptDown.x - ptMove.x,
                    ptMove.y - ptDown.y);
                g.drawOval(
                    ptMove.x,
                    ptDown.y,
                    ptDown.x - ptMove.x,
                    ptMove.y - ptDown.y);
            }
            else
            {
                g.drawRect(
                    ptMove.x,
                    ptMove.y,
                    ptDown.x - ptMove.x,
                    ptDown.y - ptMove.y);
                g.drawOval(
                    ptMove.x,
                    ptMove.y,
                    ptDown.x - ptMove.x,
                    ptDown.y - ptMove.y);
            }
        }        ptMoveOld = ptMove;
        strStatus =
            ptDown.x
                + ", "
                + ptDown.y
                + "  "
                + Math.abs(ptDown.x - ptMove.x)
                + ", "
                + Math.abs(ptDown.y - ptMove.y);
        lblStatus.setText(strStatus);
    }
}你也可以看看JAVA自带的演示DEMO!

Answer 3

对，看看jdk自带的DEMO，内容很丰富呀.