Question

我在JCreator Pro版本5.10中的JavaWorkspace下创建了一个名为“LabelTest”的项目

在项目文件夹中，我添加了文件LabelFrame.java，LabelTest.java和来自Deitel的图标bug1.png“java如何编程”第8版第14章图6和7

项目建设成功但不运行。以下是错误：

Exception in thread "main" java.lang.NullPointerException
    at javax.swing.ImageIcon.<init>(ImageIcon.java:217)
    at labeltest.LabelFrame.<init>(LabelFrame.java:30)
    at labeltest.LabelTest.main(LabelTest.java:11)

和代码：

// Fig. 14.6: LabelFrame.java
// Demonstrating the JLabel class.
//package labeltest;

import java.awt.FlowLayout; // specifies how components are arranged
import javax.swing.JFrame; // provides basic window features
import javax.swing.JLabel; // displays text and images
import javax.swing.SwingConstants; // common constants used with Swing
import javax.swing.Icon; // interface used to manipulate images
import javax.swing.ImageIcon; // loads images

public class LabelFrame extends JFrame 
{
   private JLabel label1; // JLabel with just text
   private JLabel label2; // JLabel constructed with text and icon
   private JLabel label3; // JLabel with added text and icon

   // LabelFrame constructor adds JLabels to JFrame
   public LabelFrame()
   {
      super( "Testing JLabel" );
      setLayout( new FlowLayout() ); // set frame layout

      // JLabel constructor with a string argument
      label1 = new JLabel( "Label with text" );
      label1.setToolTipText( "This is label1" );
      add( label1 ); // add label1 to JFrame

      // JLabel constructor with string, Icon and alignment arguments
      Icon bug = new ImageIcon( getClass().getResource( "bug1.png" ) );
      label2 = new JLabel( "Label with text and icon", bug, 
         SwingConstants.LEFT );
      label2.setToolTipText( "This is label2" );
      add( label2 ); // add label2 to JFrame

      label3 = new JLabel(); // JLabel constructor no arguments
      label3.setText( "Label with icon and text at bottom" );
      label3.setIcon( bug ); // add icon to JLabel
      label3.setHorizontalTextPosition( SwingConstants.CENTER );
      label3.setVerticalTextPosition( SwingConstants.BOTTOM );
      label3.setToolTipText( "This is label3" );
      add( label3 ); // add label3 to JFrame
   } // end LabelFrame constructor
} // end class LabelFrame


// Fig. 14.7: LabelTest.java
// Testing LabelFrame.
//package labeltest;

import javax.swing.JFrame;

public class LabelTest 
{
   public static void main( String[] args )
   { 
      LabelFrame labelFrame = new LabelFrame(); // create LabelFrame
      labelFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
      labelFrame.setSize( 260, 180 ); // set frame size
      labelFrame.setVisible( true ); // display frame
   } // end main
} // end class LabelTest

Answer 1

您的程序无法运行编译，因为它在此行遇到异常：

Icon bug = new ImageIcon( getClass().getResource( "bug1.png" ) );

该异常是无法找到名为bug1.png的文件的结果。

确保使用正确的 路径名 和 文件名 。

GUI代码无法运行 - 来自Deitel的书

1 个答案: