我一直在努力创建一个根据用户输入计算三角函数的gui。我在GUI部分取得了成功，但是我写的用于使用继承来保存信息的类似乎搞砸了，因为当我运行它时会出现错误说：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.ImageIcon.<init>(ImageIcon.java:181)
at TrigCalc.TrigCalcGUI$CalcButtonListener.actionPerformed(TrigCalcGUI.java:191)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6288)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6053)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4651)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4481)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:643)
at java.awt.EventQueue.access$000(EventQueue.java:84)
at java.awt.EventQueue$1.run(EventQueue.java:602)
at java.awt.EventQueue$1.run(EventQueue.java:600)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:616)
at java.awt.EventQueue$2.run(EventQueue.java:614)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:613)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
我更改了程序的顺序以便于阅读：
public class TrigCalcCon
{
public double sine;
public double cosine;
public double tangent;
public TrigCalcCon(double sin, double cos, double tan)
{
sine = sin;
cosine = cos;
tangent = tan;
}
public void setSin(double s)
{
sine = s;
}
public void setCos(double cs)
{
cosine = cs;
}
public void setTan(double t)
{
tangent = t;
}
public void set(double s, double cs, double t)
{
sine = s;
cosine = cs;
tangent = t;
}
public double getSin()
{
return Math.sin(sine);
}
public double getCos()
{
return Math.cos(cosine);
}
public double getTan()
{
return Math.tan(tangent);
}
}
这是继承类。
public class ArcTrigCalcCon extends TrigCalcCon
{
// Instance Variables
public double cosecant;
public double secant;
public double cotangent;
public ArcTrigCalcCon(double s, double cs, double t)
{
// Inherit from the Trig Calc class
super(s, cs, t);
cosecant = 1/s;
secant = 1/cs;
cotangent = 1/t;
}
public void setCsc(double csc)
{
cosecant = csc;
}
public void setSec(double sc)
{
secant = sc;
}
public void setCot(double ct)
{
cotangent = ct;
}
}
这是运行gui的演示类：
public class TrigCalcGUI extends JFrame implements ActionListener
{
// Instance Variables
private String input;
private double s = 0, cs = 0, t = 0;
private JPanel mainPanel, sinPanel, cosPanel, tanPanel, cscPanel, secPanel,
cotPanel, buttonPanel, inputPanel, displayPanel; // Panel Display
private JLabel inputLabel;
private JTextField sinTF, cosTF, tanTF, secTF,
cscTF, cotTF, inputTF; //Text Fields for sin, cos, and tan, and inverse
private JButton calcButton, clearButton; // Calculate and Exit Buttons
// Object
ArcTrigCalcCon trC = new ArcTrigCalcCon(s, cs, t);
public TrigCalcGUI()
{
// title bar text.
super("Trig Calculator");
// Corner exit button action.
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Create main panel to add each panel to
mainPanel = new JPanel();
mainPanel.setLayout(new GridLayout(3,2));
displayPanel = new JPanel();
displayPanel.setLayout(new GridLayout(3,2));
// Assign Panel to each variable
inputPanel = new JPanel();
sinPanel = new JPanel();
cosPanel = new JPanel();
tanPanel = new JPanel();
cscPanel = new JPanel();
secPanel = new JPanel();
cotPanel = new JPanel();
buttonPanel = new JPanel();
// Call each constructor
buildInputPanel();
buildSinCosTanPanels();
buildCscSecCotPanels();
buildButtonPanel();
// Add each panel to content pane
displayPanel.add(sinPanel);
displayPanel.add(cscPanel);
displayPanel.add(cosPanel);
displayPanel.add(secPanel);
displayPanel.add(tanPanel);
displayPanel.add(cotPanel);
// Add three content panes to GUI
mainPanel.add(inputPanel, BorderLayout.NORTH);
mainPanel.add(displayPanel, BorderLayout.CENTER);
mainPanel.add(buttonPanel, BorderLayout.SOUTH);
//add mainPanel
this.add(mainPanel);
// size of window to content
this.pack();
// display window
setVisible(true);
}
public static void main(String[] args)
{
new TrigCalcGUI();
}
private void buildInputPanel()
{
inputLabel = new JLabel("Enter a Value: ");
inputTF = new JTextField(5);
inputPanel.add(inputLabel);
inputPanel.add(inputTF);
}
// Building Constructor for sinPanel cosPanel, and tanPanel
private void buildSinCosTanPanels()
{
// Set layout and border for sinPanel
sinPanel.setLayout(new GridLayout(2,2));
sinPanel.setBorder(BorderFactory.createTitledBorder("Sine"));
//
sinTF = new JTextField(5);
sinTF.setEditable(false);
sinPanel.add(sinTF);
// Set layout and border for cosPanel
cosPanel.setLayout(new GridLayout(2,2));
cosPanel.setBorder(BorderFactory.createTitledBorder("Cosine"));
cosTF = new JTextField(5);
cosTF.setEditable(false);
cosPanel.add(cosTF);
// Set layout and border for tanPanel
tanPanel.setLayout(new GridLayout(2,2));
tanPanel.setBorder(BorderFactory.createTitledBorder("Tangent"));
tanTF = new JTextField(5);
tanTF.setEditable(false);
tanPanel.add(tanTF);
}
// Building Constructor for cscPanel secPanel, and cotPanel
private void buildCscSecCotPanels()
{
// Set layout and border for cscPanel
cscPanel.setLayout(new GridLayout(2,2));
cscPanel.setBorder(BorderFactory.createTitledBorder("Cosecant"));
//
cscTF = new JTextField(5);
cscTF.setEditable(false);
cscPanel.add(cscTF);
// Set layout and border for secPanel
secPanel.setLayout(new GridLayout(2,2));
secPanel.setBorder(BorderFactory.createTitledBorder("Secant"));
secTF = new JTextField(5);
secTF.setEditable(false);
secPanel.add(secTF);
// Set layout and border for cotPanel
cotPanel.setLayout(new GridLayout(2,2));
cotPanel.setBorder(BorderFactory.createTitledBorder("Cotangent"));
cotTF = new JTextField(5);
cotTF.setEditable(false);
cotPanel.add(cotTF);
}
private void buildButtonPanel()
{
// Create buttons and add events
calcButton = new JButton("Calculate");
calcButton.addActionListener(new CalcButtonListener());
clearButton = new JButton("Clear");
clearButton.addActionListener(new ClearButtonListener());
buttonPanel.add(calcButton);
buttonPanel.add(clearButton);
}
@Override
public void actionPerformed(ActionEvent e)
{
}
private class CalcButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent ae)
{
// Declare boolean variable
boolean incorrect = true;
// Set input variable to input text field text
input = inputTF.getText();
ImageIcon newIcon;
ImageIcon frowny = new
ImageIcon(TrigCalcGUI.class.getResource("/Sad_Face.png"));
Image gm = frowny.getImage();
Image newFrowny = gm.getScaledInstance(100, 100,
java.awt.Image.SCALE_FAST);
newIcon = new ImageIcon(newFrowny);
// If boolean is true, throw exception
if(incorrect)
{
try{Double.parseDouble(input); incorrect = false;}
catch(NumberFormatException nfe)
{
String s = "Invalid Input "
+ "/n Input Must Be a Numerical value."
+ "/nPlease Press Ok and Try Again";
JOptionPane.showMessageDialog(null, s, "Invalid",
JOptionPane.ERROR_MESSAGE, newIcon);
inputTF.setText("");
inputTF.requestFocus();
}
}
// If boolean is not true, proceed with output
if (incorrect != true)
{
/* Set each text field's output to the String double value
* of inputTF
*/
sinTF.setText(input);
cosTF.setText(input);
tanTF.setText(input);
cscTF.setText(input);
secTF.setText(input);
cotTF.setText(input);
}
}
}
/**
* Private inner class that handles the event when
* the user clicks the Exit button.
*/
private class ClearButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent ae)
{
// Clear field
sinTF.setText("");
cosTF.setText("");
tanTF.setText("");
cscTF.setText("");
secTF.setText("");
cotTF.setText("");
// Clear textfield and set cursor focus to field
inputTF.setText("");
inputTF.requestFocus();
}
}
}
如果可能的话，我可能需要一些帮助，因为我是一个视觉学习者。我知道这可能很简单，因为我是初学者，所以有点难以理解。
答案 0 :(得分：0)
您将变量创建为“Double”，但定义了使用它们接受“double”参数的函数。您可以至少在3个方向上解决此问题;将变量定义更改为“double”或将函数定义更改为使用“Double”，或单独保留声明并使用双精度的doubleValue调用函数。
ArcTrigCalcCon trC = new ArcTrigCalcCon(s.doubleValue(), cs.doubleValue(), t.doubleValue());
答案 1 :(得分：0)
就在这里：
ArcTrigCalcCon trC = new ArcTrigCalcCon(s, cs, t);
您正在尝试使用TrigCalcCon构造函数创建新的ArcTrigCalcCon对象，并且构造函数不会在Java中继承。您必须创建一个构造函数，其参数与超类构造函数相同，并将它们与super(s, cs, t);一起传递，或者使用您提供的6个双构造函数。
答案 2 :(得分：0)
ArcTrigCalcCon的构造函数有六个参数，但实际上只使用其中三个参数。在该构造函数中根本不使用最后三个参数，因此如果您愿意，可以删除它们。
现在，当您尝试在ArcTrigCalcCon类中创建TrigCalcGui对象时，您尝试仅将三个参数传递给构造函数，而不是全部六个;这就是编译器给你一个错误的原因。你可以做两件事之一
任何一种行动都会使错误消失。