我已经用Java编程了一段时间但是从来没有真正使用swing包.我目前正在为A.I.设计GUI.呼叫和响应程序,尽管我一直在做的其余部分相对复杂(至少对我来说),这个图像加载问题,实现起来非常简单,让我感到难过.

如果不是在包中,下面的类可以工作,这真的让我感到困惑.我尝试了几种不同的实现建议(一个来自Head First Java,一个来自docs.oracle.com教程,另一个来自http://leepoint.net/notes-java/GUI-lowlevel/graphics/45imageicon.html建议).

package CaRII;

import java.util.*;

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class P{

public static void main(String [] args){

P p = new P();

p.go();

}

public void go(){

JFrame frame = new JFrame("CaRRI: Call and Response Intelligent Improviser");

PBackground mainPanel = new PBackground();

frame.getContentPane().add(BorderLayout.CENTER, mainPanel);

frame.setSize(800,500);

frame.setVisible(true);

}

}

package CaRII;

import java.awt.*;

import javax.swing.*;

public class PBackground extends JPanel{

public Image backgroundImage;

public PBackground(){

backgroundImage = Toolkit.getDefaultToolkit().createImage("CaRIIBackGround.jpg");

}

public PBackground(LayoutManager layout){

backgroundImage = Toolkit.getDefaultToolkit().createImage("CaRIIBackGround.jpg");

}

public void paint(Graphics g){

g.drawImage(backgroundImage,0,0,null);

}

}

就像我说的奇怪的是,如果这两个类都在CaRRI包中,它就不显示图像;但是如果我在没有包声明的情况下编译并运行它们就可以正常运行(在窗口调整大小之前,这个图像没有加载…但是我已经在网上找到了这样的解决方案,所以一旦我在其中加载它,我就可以对它进行排序包).我一直在写XCode和JEdit,图像存储在源包内的包文件夹中(/src/CaRII/P.java … /src/CaRII/CaRIIBackGround.jpg),我也尝试将图像存储在/ src /中使用的资源文件夹

ImageIcon(getClass().getResource("/resources/CaRIIBackGround.jpg)).getImage();

但这会在运行时导致另一个错误

Exception in thread "main" java.lang.NullPointerException

at javax.swing.ImageIcon.(ImageIcon.java:181)

at CaRII.PBackground.(PBackground.java:19)

at CaRII.P.go(P.java:21)

at CaRII.P.main(P.java:15)

任何帮助都会非常感激,尽管它很简单,但是我整个上午一直困扰着我,还有很多其他的课程要写.

最佳答案

package CaRII;

import java.awt.*;

import java.awt.image.BufferedImage;

import javax.swing.*;

import java.net.URL;

import javax.imageio.ImageIO;

public class P{

public static void main(String [] args){

SwingUtilities.invokeLater(new Runnable() {

public void run() {

P p = new P();

p.go();

}

});

}

public void go(){

try {

JFrame frame = new JFrame("CaRRI: Call and Response Intelligent Improviser");

frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

PBackground mainPanel = new PBackground();

frame.getContentPane().add(BorderLayout.CENTER, mainPanel);

//frame.setSize(800,500);

frame.pack();

frame.setMinimumSize(frame.getSize());

frame.setLocationByPlatform(true);

frame.setVisible(true);

} catch(Exception e) {

e.printStackTrace();

}

}

}

class PBackground extends JPanel{

public BufferedImage backgroundImage;

public PBackground() throws Exception {

URL url = new URL("http://desmond.imageshack.us/Himg189/" +

"scaled.php?server=189&filename=cariibackground.jpg&res=medium");

// You might form that URL using something like..

//URL url = this.getClass().getResource("/CaRIIBackGround.jpg");

backgroundImage = ImageIO.read(url);

Dimension d = new Dimension(

backgroundImage.getWidth(),

backgroundImage.getHeight());

setPreferredSize(d);

}

/* What was this supposed to achieve?

public PBackground(LayoutManager layout){

backgroundImage = Toolkit.getDefaultToolkit().createImage("CaRIIBackGround.jpg");

}

*/

// Don't override paint() in a Swing panel!

//public void paint(Graphics g){

@Override

public void paintComponent(Graphics g) {

// USE the ImageObserver!

//g.drawImage(backgroundImage,0,0,null);

g.drawImage(backgroundImage,0,0,getWidth(),getHeight(),this);

}

}