一个很奇怪的错误

Question

先看程序
public class Frame1 extends JFrame {
    JPanel contentPane;
    DefaultTableModel dtModel = new DefaultTableModel();
    JTable jTable1 = new JTable(dtModel);
    JScrollPane jScrollPane1 = new JScrollPane();
    public Frame1() {
        try {
            setDefaultCloseOperation(EXIT_ON_CLOSE);
            jbInit();
            dtModel.addColumn("asdf");//把这句注释掉就正常了。
        } catch (Exception exception) {
            exception.printStackTrace();
        }
    }    /**
     * Component initialization.
     *
     * @throws java.lang.Exception
     */
    private void jbInit() throws Exception {
        contentPane = (JPanel) getContentPane();
        contentPane.setLayout(null);
        setSize(new Dimension(500, 500));
        setTitle("Frame Title");
        jScrollPane1.setBounds(new Rectangle(76, 111, 245, 137));
        contentPane.add(jScrollPane1);
        
        jScrollPane1.getViewport().add(jTable1);
    }
}
程序一运行就报错，说是空指针异常，可奇怪的是dtModel.addColumn("asdf");这句话没有错啊，我在另一个程序里也这样写，结果就能运行通过这是什么原因？？

Answer 1

public static Integer valueOf(int i) {
final int offset = 128;
if (i >= -128 && i <= 127) { // must cache 
    return IntegerCache.cache[i + offset];
}
        return new Integer(i);
    }private static class IntegerCache {
private IntegerCache(){} static final Integer cache[] = new Integer[-(-128) + 127 + 1]; static {
    for(int i = 0; i < cache.length; i++)
cache[i] = new Integer(i - 128);
}
    }

Answer 2

可我用的是JBUILDER2006就是报错啊，错误信息如下：
C:\Borland\JBuilder2006\jdk1.5\bin\javaw -classpath "E:\JavaProject\TableTest\classes;C:\Borland\JBuilder2006\jdk1.5\lib\jconsole.jar;C:\Borland\JBuilder2006\jdk1.5\lib\tools.jar;C:\Borland\JBuilder2006\jdk1.5\lib\htmlconverter.jar;C:\Borland\JBuilder2006\jdk1.5\lib\dt.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\jsse.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\im\indicim.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\im\thaiim.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\jce.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\deploy.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\javaws.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\charsets.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\rt.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\ext\dnsns.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\ext\sunpkcs11.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\ext\localedata.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\ext\sunjce_provider.jar;C:\Borland\JBuilder2006\jdk1.5\jre\lib\plugin.jar"  tabletest.Application1 
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.border.EmptyBorder.<init>(EmptyBorder.java:54)
at com.sun.java.swing.plaf.windows.WindowsTableHeaderUI$XPDefaultRenderer.getTableCellRendererComponent(WindowsTableHeaderUI.java:120)
at javax.swing.plaf.basic.BasicTableHeaderUI.getHeaderRenderer(BasicTableHeaderUI.java:387)
at javax.swing.plaf.basic.BasicTableHeaderUI.getHeaderHeight(BasicTableHeaderUI.java:421)
at javax.swing.plaf.basic.BasicTableHeaderUI.createHeaderSize(BasicTableHeaderUI.java:447)
at javax.swing.plaf.basic.BasicTableHeaderUI.getPreferredSize(BasicTableHeaderUI.java:478)
at javax.swing.JComponent.getPreferredSize(JComponent.java:1582)
at javax.swing.ViewportLayout.preferredLayoutSize(ViewportLayout.java:78)
at java.awt.Container.preferredSize(Container.java:1558)
at java.awt.Container.getPreferredSize(Container.java:1543)
at javax.swing.JComponent.getPreferredSize(JComponent.java:1584)
at javax.swing.ScrollPaneLayout.layoutContainer(ScrollPaneLayout.java:702)
at java.awt.Container.layout(Container.java:1401)
at java.awt.Container.doLayout(Container.java:1390)
at java.awt.Container.validateTree(Container.java:1473)
at java.awt.Container.validateTree(Container.java:1480)
at java.awt.Container.validateTree(Container.java:1480)
at java.awt.Container.validateTree(Container.java:1480)
at java.awt.Container.validateTree(Container.java:1480)
at java.awt.Container.validate(Container.java:1448)
at java.awt.Window.show(Window.java:515)
at java.awt.Component.show(Component.java:1300)
at java.awt.Component.setVisible(Component.java:1253)
at tabletest.Application1.<init>(Application1.java:47)
at tabletest.Application1$1.run(Application1.java:65)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)