Java 当我尝试运行这段代码几分钟时,Eclipse一直冻结,然后显示NullPointerException
我有一个程序,应该显示一个4 x元素的列表。我不太擅长这些列表,所以我结合几个例子做了很多研究。最后,我为它创建了一个名为Java 当我尝试运行这段代码几分钟时,Eclipse一直冻结,然后显示NullPointerException,java,eclipse,swing,nullpointerexception,celllist,Java,Eclipse,Swing,Nullpointerexception,Celllist,我有一个程序,应该显示一个4 x元素的列表。我不太擅长这些列表,所以我结合几个例子做了很多研究。最后,我为它创建了一个名为TabListCellRenderer的类: import java.awt.*; import java.util.*; import javax.swing.*; import javax.swing.border.*; class TabListCellRenderer extends JLabel implements ListCellRenderer{
TabListCellRenderer
的类:
import java.awt.*;
import java.util.*;
import javax.swing.*;
import javax.swing.border.*;
class TabListCellRenderer extends JLabel implements ListCellRenderer{
protected static Border m_noFocusBorder;
protected FontMetrics m_fm = null;
protected Insets m_insets = new Insets(0, 0, 0, 0);
protected int m_defaultTab = 50;
protected int[] m_tabs = null;
public TabListCellRenderer() {
super();
m_noFocusBorder = new EmptyBorder(1, 1, 1, 1);
setOpaque(true);
setBorder(m_noFocusBorder);
}
public Component getListCellRendererComponent(JList list,Object value, int index, boolean isSelected, boolean cellHasFocus){
setText(value.toString());
setBackground(isSelected ? list.getSelectionBackground() : list.getBackground());
setForeground(isSelected ? list.getSelectionForeground() : list.getForeground());
setFont(list.getFont());
setBorder((cellHasFocus) ? UIManager.getBorder("List.focusCellHighlightBorder") : m_noFocusBorder);
return this;
}
public void setDefaultTab(int defaultTab) {
m_defaultTab = defaultTab;
}
public int getDefaultTab() {
return m_defaultTab;
}
public void setTabs(int[] tabs) {
m_tabs = tabs;
}
public int[] getTabs() {
return m_tabs;
}
public int getTab(int index) {
if (m_tabs == null)
return m_defaultTab*index;
int len = m_tabs.length;
if (index>=0 && index<len)
return m_tabs[index];
return m_tabs[len-1] + m_defaultTab*(index-len+1);
}
public void paint(Graphics g) {
m_fm = g.getFontMetrics();
g.setColor(getBackground());
g.fillRect(0, 0, getWidth(), getHeight());
getBorder().paintBorder(this, g, 0, 0, getWidth(), getHeight());
g.setColor(getForeground());
g.setFont(getFont());
m_insets = getInsets();
int x = m_insets.left;
int y = m_insets.top + m_fm.getAscent();
StringTokenizer st = new StringTokenizer(getText(), "\t");
while (st.hasMoreTokens()){
String sNext = st.nextToken();
g.drawString(sNext, x, y);
x += m_fm.stringWidth(sNext);
if (!st.hasMoreTokens())
break;
int index = 0;
while (x >= getTab(index))
index++;
x = getTab(index);
}
}
}
如果我运行这3行,我的Eclipse会冻结几分钟(3-5),然后说这3行中的最后一行导致了NullPointerException
:
Exception in thread "main" java.lang.NullPointerException
at classe_di_interfaccia.MyPanel.<init>(MyPanel.java:76)
at classe_di_interfaccia.TestClass.main(TestClass.java:9)
JFrame:
import java.awt.*;
import javax.swing.*;
public class MyFrame extends JFrame {
public MyFrame(){
super();
setBounds(100,100,350,600);
}
public MyFrame(String titolo){
super(titolo);
setBounds(100,100, 350,600);
}
}
要测试的类:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.JTabbedPane;
public class Test{
public static void main(String[] v){
JFrame f = new MyFrame("Una Mensola Automatico");
Container c = f.getContentPane();
JPanel panel = new PanelGrafica();
f.setResizable(false);
f.show();
}
}
这是什么:listaAnimali.setCellRenderer(渲染器);第76行:出错的那一行。它用于向列表显示我相信它有多少个单元格(我从互联网上获得了这段代码,但在我来到这里之前,我已经把所有的信息都记录下来了)。为了更快地获得更好的帮助,请发布一个or。@andrewhompson在这里,我为您准备了一些测试类MyPanel.java的源代码行76中有什么?在classe_di_interfacecia.MyPanel.(MyPanel.java:76)中标识为NPE的源代码。您发布的类
面板
似乎与MyPanel
不同。因为Panel.java
包含类PanelGrafica
的构造函数。正如Andrew所说,发布代码来说明您的问题。
import java.awt.*;
import javax.swing.*;
public class MyFrame extends JFrame {
public MyFrame(){
super();
setBounds(100,100,350,600);
}
public MyFrame(String titolo){
super(titolo);
setBounds(100,100, 350,600);
}
}
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.JTabbedPane;
public class Test{
public static void main(String[] v){
JFrame f = new MyFrame("Una Mensola Automatico");
Container c = f.getContentPane();
JPanel panel = new PanelGrafica();
f.setResizable(false);
f.show();
}
}