Question

java初学者 求教怎么在窗口中添加一张图片

package java525;

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

public class MainWindow extends JFrame implements ActionListener {

JMenuBar menuBar;//菜单条
JMenu menu1, menu2, menu3, menu4;//菜单
JMenuItem m11, m12, m13;//菜单项
JMenuItem m21, m22, m23;
JMenuItem m31, m32, m33;
JMenuItem m41, m42;

public MainWindow() {
createMenu();
setTitle("学生管理系统"); //设置窗口标题
setIconImage((new ImageIcon("icon.gif")).getImage()); //设置图标
setSize(600, 400);//设置窗口大小
Dimension size = Toolkit.getDefaultToolkit().getScreenSize();//取屏幕大小
setLocation((size.width - getWidth()) / 2, (size.height - getHeight()) / 2);
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); //设置关闭行为
setVisible(true);//使窗口可见
this.setExtendedState(JFrame.MAXIMIZED_BOTH);

}

想在 "学生管理系统"这个大窗口下添加一张图片

Answer 1

//注意：
//当前目录下要有一个p.jpg文件
//压缩这个文件使它的大小尽量小，最好只有几十KB
//否则无法显示背景图片
package java525;

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

public class MainWindow extends JFrame implements ActionListener {
JMenuBar menuBar;//菜单条
JMenu menu1, menu2, menu3, menu4;//菜单
JMenuItem m11, m12, m13;//菜单项
JMenuItem m21, m22, m23;
JMenuItem m31, m32, m33;
JMenuItem m41, m42;
Image pic;
public static void main(String[] args) {
new MainWindow();
}
public MainWindow() {
pic=Toolkit.getDefaultToolkit().getImage("p.jpg");
MediaTracker t=new MediaTracker(this);
t.addImage(pic,1);
try
{
t.waitForID(1);
}
catch(Exception e)
{

}
//createMenu();
setTitle("学生管理系统"); //设置窗口标题
setIconImage((new ImageIcon("icon.gif")).getImage()); //设置图标
setSize(600, 400);//设置窗口大小
Dimension size = Toolkit.getDefaultToolkit().getScreenSize();//取屏幕大小
setLocation((size.width - getWidth()) / 2, (size.height - getHeight()) / 2);
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); //设置关闭行为
setVisible(true);//使窗口可见
//this.setExtendedState(JFrame.MAXIMIZED_BOTH);
}
public void actionPerformed(ActionEvent e) {

}
public void paint(Graphics g) {
super.paint(g);
g.drawImage(pic,0,0,null);
}
}

Answer 2

import javax.imageio.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
/**
 * 格子绘图演示
 * @author hardneedl
 */
final class P extends JFrame{
    private static final Dimension SIZE = new Dimension(600,400);

    public Dimension getMinimumSize() {return SIZE;}
    public Dimension getMaximumSize() {return SIZE;}
    public Dimension getPreferredSize() {return SIZE;}

    public String getTitle() {return "画笔绘图示意";}

    private JComponent canvas;

    private P() throws HeadlessException {
        super();
        init();
        addListeners();
        doLay();
    }

    private void init() {

        canvas = new MyCanvas() {
            private Brush b;

            Brush getBrush() {
                try {
                    return b == null ?
                        b =  new PictureBrush(ImageIO.read(new File(System.getProperty("app.picture"))))
                        :
                        b;
                } catch (IOException e) {
                    e.printStackTrace();
                }
                return null;
            }
        };

    }

    private void doLay(){
        getContentPane().add(canvas, BorderLayout.CENTER);
        pack();
        setVisible(true);
    }

    private void addListeners(){
        addWindowListener(new WindowAdapter() {

            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
    }

    public static void main(String... args) {
        SwingUtilities.invokeLater(P::new);
    }

    /*抽象画布*/
    abstract private static class MyCanvas extends JComponent {

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            getBrush().paint(g);
        }

        abstract Brush getBrush();
    }

    /*画笔*/
    private interface Brush {
        void paint(Graphics g);
    }

    /*图片画笔*/
    private static class PictureBrush implements Brush, Observer {
        private Image img;
        private PictureBrush(Image img) {
            this.img = img;
        }

        public void paint(Graphics g) {
            if (img == null) return;
            Graphics g2 = g.create();

            g2.drawImage(img, 0, 0, null);
            g2.dispose();
        }

        public void update(Observable o, Object arg) {}
    }
}