Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at SelectUnitFrame.<init>(SelectUnitFrame.java:112)
at CoolingTowerFrame$ButtonListener.actionPerformed(CoolingTowerFrame.java:184)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
代码很长但我可以编辑这篇文章并添加它是否有帮助
我认为代码因此无效
[第112行] tableButton.setRolloverEnabled(false);
我需要禁用翻转的原因是当按下按钮时按下按钮它不会返回到原始图像。如果有任何修复，那也可能有效。
继承人代码：
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
public class SelectUnitFrame extends JFrame
{
public JLabel showNumbersLabel;
public JPanel showPanel = new JPanel();
public JButton tableButton;
public JPanel buttonPanel = new JPanel();
public JButton goBackButton = new JButton("Change Variables");
public JButton exitButton = new JButton("Done");
public JButton nextButton = new JButton(">");
public JButton prevButton = new JButton("<");
public int fRate;
public int wbTemp;
public int r;
public int a;
public int rcTons;
public int count;
public String [] tablesFor80 = {"80F_FG2003.GIF", "80F_FG2004.GIF", "80F_FG2005.GIF", "80F_FG2007.GIF", "80F_FG2009.GIF", "80F_FG2011.GIF", "80F_FG2015.GIF"};
public String [] tablesFor78 = {"78F_FG2003.GIF", "78F_FG2004.GIF", "78F_FG2005.GIF", "78F_FG2007.GIF", "78F_FG2009.GIF", "78F_FG2011.GIF", "78F_FG2015.GIF"};
public String [] tablesFor76 = {"76F_FG2003.GIF", "76F_FG2004.GIF", "76F_FG2005.GIF", "76F_FG2007.GIF", "76F_FG2009.GIF", "76F_FG2011.GIF", "76F_FG2015.GIF"};
public String [] tablesFor74 = {"74F_FG2003.GIF", "74F_FG2004.GIF", "74F_FG2005.GIF", "74F_FG2007.GIF", "74F_FG2009.GIF", "74F_FG2011.GIF", "74F_FG2015.GIF"};
public String [] tablesFor72 = {"72F_FG2003.GIF", "72F_FG2004.GIF", "72F_FG2005.GIF", "72F_FG2007.GIF", "72F_FG2009.GIF", "72F_FG2011.GIF", "72F_FG2015.GIF"};
public String [] tablesFor70 = {"70F_FG2003.GIF", "70F_FG2004.GIF", "70F_FG2005.GIF", "70F_FG2007.GIF", "70F_FG2009.GIF", "70F_FG2011.GIF", "70F_FG2015.GIF"};
public String [] tablesFor68 = {"68F_FG2003.GIF", "68F_FG2004.GIF", "68F_FG2005.GIF", "68F_FG2007.GIF", "68F_FG2009.GIF", "68F_FG2011.GIF", "68F_FG2015.GIF"};
public ImageIcon tablePicture;
public SelectUnitFrame(int flowRate, int wetBulbTemp, int roundedCoolingTons, int approach, int range)
{
super("Unit Selected");
Toolkit toolkit = Toolkit.getDefaultToolkit();
Dimension dimensions = toolkit.getScreenSize();
int x = (dimensions.width - 750)/2;
int y = (dimensions.height - 350)/2;
setBounds(x, y, 750, 350);
setVisible(true);
setResizable(false);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
goBackButton.addActionListener(new ButtonListener());
exitButton.addActionListener(new ButtonListener());
nextButton.addActionListener(new ButtonListener());
prevButton.addActionListener(new ButtonListener());
fRate = flowRate;
wbTemp = wetBulbTemp;
r = range;
a = approach;
rcTons = roundedCoolingTons;
buttonPanel.add(goBackButton);
buttonPanel.add(exitButton);
add(buttonPanel, BorderLayout.SOUTH);
showNumbersLabel = new JLabel("Wet Bulb: " + wbTemp + "(deg)F " + "Range: " + r + " Approach: " + a + " Tons/GPM: " + rcTons + "/" + fRate);
showPanel.add(showNumbersLabel);
add(showPanel, BorderLayout.NORTH);
if ((wbTemp >= 79) && (wbTemp < 82))
{
tempSelection80(flowRate, wetBulbTemp, roundedCoolingTons, approach, range);
}
else if ((wbTemp < 79 ) && (wbTemp >= 77))
{
tempSelection78(flowRate, wetBulbTemp, roundedCoolingTons, approach, range);
}
else if ((wbTemp < 77) && (wbTemp >= 75))
{
tempSelection76(flowRate, wetBulbTemp, roundedCoolingTons, approach, range);
}
else if ((wbTemp < 75) && (wbTemp >= 73))
{
tempSelection74(flowRate, wetBulbTemp, roundedCoolingTons, approach, range);
}
else if ((wbTemp < 73) && (wbTemp >= 71))
{
tempSelection72(flowRate, wetBulbTemp, roundedCoolingTons, approach, range);
}
else if ((wbTemp < 71) && (wbTemp >= 69))
{
tempSelection70(flowRate, wetBulbTemp, roundedCoolingTons, approach, range);
}
else if ((wbTemp < 69) && (wbTemp >= 67))
{
tempSelection68(flowRate, wetBulbTemp, roundedCoolingTons, approach, range);
}
else
{
tableButton = new JButton("Cooling Tower Cannot Handle Temperatures In This Wet Bulb");
}
tableButton.setRolloverEnabled(false);
add(nextButton, BorderLayout.EAST);
add(prevButton, BorderLayout.WEST);
add(tableButton, BorderLayout.CENTER);
}
private class ButtonListener implements ActionListener
{
@Override
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == goBackButton)
{
dispose();
}
else if (e.getSource() == exitButton)
{
System.exit(0);
}
else if (e.getSource() == nextButton)
{
String t = tableButton.getText();
tableButton.updateUI();
String s = ((ImageIcon)tableButton.getIcon()).toString();
if ((wbTemp >= 79) && (wbTemp < 82))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor80[i]))
{
if (i == 6)
{
count = 0;
}
else
{
count = (i+1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor80[count], tablesFor80[count]));
}
else if ((wbTemp < 79 ) && (wbTemp >= 77))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor78[i]))
{
if (i == 6)
{
count = 0;
}
else
{
count = (i+1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor78[count], tablesFor78[count]));
}
else if ((wbTemp < 77) && (wbTemp >= 75))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor76[i]))
{
if (i == 6)
{
count = 0;
}
else
{
count = (i+1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor76[count], tablesFor76[count]));
}
else if ((wbTemp < 75) && (wbTemp >= 73))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor74[i]))
{
if (i == 6)
{
count = 0;
}
else
{
count = (i+1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor74[count], tablesFor74[count]));
}
else if ((wbTemp < 73) && (wbTemp >= 71))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor72[i]))
{
if (i == 6)
{
count = 0;
}
else
{
count = (i+1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor72[count], tablesFor72[count]));
}
else if ((wbTemp < 71) && (wbTemp >= 69))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor70[i]))
{
if (i == 6)
{
count = 0;
}
else
{
count = (i+1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor70[count], tablesFor70[count]));
}
else if ((wbTemp < 69) && (wbTemp >= 67))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor68[i]))
{
if (i == 6)
{
count = 0;
}
else
{
count = (i+1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor68[count], tablesFor68[count]));
}
tableButton.setRolloverEnabled(false);
add(tableButton, BorderLayout.CENTER);
}
else if (e.getSource() == prevButton)
{
String t = tableButton.getText();
tableButton.updateUI();
String s = ((ImageIcon)tableButton.getIcon()).toString();
if ((wbTemp >= 79) && (wbTemp < 82))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor80[i]))
{
if (i == 0)
{
count = 6;
}
else
{
count = (i-1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor80[count], tablesFor80[count]));
}
else if ((wbTemp < 79 ) && (wbTemp >= 77))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor78[i]))
{
if (i == 0)
{
count = 6;
}
else
{
count = (i-1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor78[count], tablesFor78[count]));
}
else if ((wbTemp < 77) && (wbTemp >= 75))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor76[i]))
{
if (i == 0)
{
count = 6;
}
else
{
count = (i-1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor76[count], tablesFor76[count]));
}
else if ((wbTemp < 75) && (wbTemp >= 73))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor74[i]))
{
if (i == 0)
{
count = 6;
}
else
{
count = (i-1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor74[count], tablesFor74[count]));
}
else if ((wbTemp < 73) && (wbTemp >= 71))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor72[i]))
{
if (i == 0)
{
count = 6;
}
else
{
count = (i-1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor72[count], tablesFor72[count]));
}
else if ((wbTemp < 71) && (wbTemp >= 69))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor70[i]))
{
if (i == 0)
{
count = 6;
}
else
{
count = (i-1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor70[count], tablesFor70[count]));
}
else if ((wbTemp < 69) && (wbTemp >= 67))
{
if (t.equals("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables."))
{
count = 0;
}
else
{
for (int i = 0; i <= 6; i++)
{
if (s.equals(tablesFor68[i]))
{
if (i == 0)
{
count = 6;
}
else
{
count = (i-1);
}
}
}
}
tableButton = new JButton(new ImageIcon(tablesFor68[count], tablesFor68[count]));
}
tableButton.setRolloverEnabled(false);
add(tableButton, BorderLayout.CENTER);
}
}
}
问题在于这个声明在一个方法中被称为它的主体对我来说太长了我无法添加它
else
{
tableButton = new JButton("Cannot Find Model for Variables Given. Adjust or Scroll to Look Through Tables.");
}
}
答案 0 :(得分：0)
tableButton为空，除非else / if / else if长列表的else部分已运行。
换句话说，如果wbTemp介于69和82之间，则会出现NullPointerException。
结论：如果tableButton = new JButton(...)介于69到82之间，则需要运行wbTemp之类的语句。
编辑
为了解决您的评论，我在下面添加了一个代码示例，其中：
我建议你阅读一下该语言的基础知识，例如the Java Tutorial
if(condition1) {
//(Block 1)
} else if(condition2) {
//(Block 2)
} else {
//(Block 3)
}