所以我一直试图弄清楚为什么我的JApplet正在启动并且没有出现任何错误，但没有任何错误显示出来。我有一个调用setup_layout（）的init（）方法，但我想我可能做错了布局。有人帮忙吗？
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.JTextArea;
public class Assignment8 extends JApplet implements ActionListener
{
public static final int WIDTH = 500;
public static final int HEIGHT = 500;
public static final int NUMBER_OF_DIGITS = 30;
private JTextArea operand, result;
private double answer = 0.0;
private JButton sevenB, eightB, nineB, divideB, fourB, fiveB, sixB, multiplyB, oneB, twoB, threeB, subtractB,
zeroB, dotB, addB, resetB, clearB, sqrtB, absB, expB;
/** public static void main(String[] args)
{
Assignment8 aCalculator = new Assignment8( );
aCalculator.setVisible(true);
}**/
public void init( )
{
setup_layout();
}
private void setup_layout() {
setSize(WIDTH, HEIGHT);
JPanel MainPanel = new JPanel();
JPanel buttonPanel = new JPanel();
JPanel calcPanel = new JPanel();
JPanel textPanel = new JPanel ();
buttonPanel.setLayout(new GridLayout(3, 4));
calcPanel.setLayout(new GridLayout(3, 3));
textPanel.setLayout(new FlowLayout());
MainPanel.setLayout(new BorderLayout());
MainPanel.setBackground(Color.red);
operand = new JTextArea();
result = new JTextArea();
operand.setEditable(false);
result.setEditable(false);
textPanel.add(operand);
textPanel.add(result);
sevenB = new JButton("7");
eightB = new JButton("8");
nineB = new JButton("9");
divideB = new JButton("/");
fourB = new JButton("4");
fiveB = new JButton("5");
sixB = new JButton("6");
multiplyB = new JButton("*");
oneB = new JButton("1");
twoB = new JButton("2");
threeB = new JButton("3");
subtractB = new JButton("-");
zeroB = new JButton("0");
dotB = new JButton(".");
addB = new JButton("+");
resetB = new JButton("Reset");
clearB = new JButton("Clear");
sqrtB = new JButton("Sqrt");
absB = new JButton("Abs");
expB = new JButton("Exp");
sevenB.addActionListener(this);
eightB.addActionListener(this);
nineB.addActionListener(this);
divideB.addActionListener(this);
fourB.addActionListener(this);
fiveB.addActionListener(this);
sixB.addActionListener(this);
multiplyB.addActionListener(this);
oneB.addActionListener(this);
twoB.addActionListener(this);
threeB.addActionListener(this);
subtractB.addActionListener(this);
zeroB.addActionListener(this);
dotB.addActionListener(this);
addB.addActionListener(this);
resetB.addActionListener(this);
clearB.addActionListener(this);
absB.addActionListener(this);
expB.addActionListener(this);
sqrtB.addActionListener(this);
buttonPanel.add(sevenB);
buttonPanel.add(eightB);
buttonPanel.add(nineB);
buttonPanel.add(fourB);
buttonPanel.add(fiveB);
buttonPanel.add(sixB);
buttonPanel.add(oneB);
buttonPanel.add(twoB);
buttonPanel.add(threeB);
buttonPanel.add(zeroB);
buttonPanel.add(dotB);
calcPanel.add(subtractB);
calcPanel.add(multiplyB);
calcPanel.add(divideB);
calcPanel.add(sqrtB);
calcPanel.add(absB);
calcPanel.add(expB);
calcPanel.add(addB);
calcPanel.add(resetB);
calcPanel.add(clearB);
MainPanel.add(buttonPanel);
MainPanel.add(calcPanel);
MainPanel.add(textPanel);
setVisible(true);
}
public void actionPerformed(ActionEvent e)
{
try
{
assumingCorrectNumberFormats(e);
}
catch (NumberFormatException e2)
{
result.setText("Error: Reenter Number.");
}
catch (DivideByZeroException e1) {
result.setText("Error: CANNOT Divide By Zero. Reenter Number.");
}
}
//Throws NumberFormatException.
public void assumingCorrectNumberFormats(ActionEvent e) throws DivideByZeroException
{
String actionCommand = e.getActionCommand( );
if (actionCommand.equals("1"))
{
int num = 1;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("2"))
{
int num = 2;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("3"))
{
int num = 3;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("4"))
{
int num = 4;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("5"))
{
int num = 5;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("6"))
{
int num = 6;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("7"))
{
int num = 7;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("8"))
{
int num = 8;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("9"))
{
int num = 9;
operand.append(Integer.toString(num));
}
else if (actionCommand.equals("0"))
{
int num = 0;
String text = operand.getText();
//double check = stringToDouble(text);
if(text.isEmpty()||text.contains(".")) {
operand.append(Integer.toString(num));
}
}
else if (actionCommand.equals("."))
{
String text = operand.getText();
if(!text.contains(".")) {
operand.append(".");
}
}
else if (actionCommand.equals("+"))
{
answer = answer + stringToDouble(operand.getText( ));
result.setText(Double.toString(answer));
operand.setText("");
}
else if (actionCommand.equals("-"))
{
answer = answer - stringToDouble(operand.getText( ));
result.setText(Double.toString(answer));
operand.setText("");
}
else if (actionCommand.equals("*"))
{
answer = answer * stringToDouble(operand.getText( ));
result.setText(Double.toString(answer));
operand.setText("");
}
else if (actionCommand.equals("/"))
{
double check = stringToDouble(operand.getText());
if(check >= -1.0e-10 && check <= 1.0e-10 ) {
throw new DivideByZeroException();
}
else {
answer = answer / stringToDouble(operand.getText( ));
result.setText(Double.toString(answer));
operand.setText("");
}
}
else if (actionCommand.equals("Sqrt"))
{
double check = stringToDouble(result.getText());
if(check < 0 ) {
throw new NumberFormatException();
}
else {
answer = Math.sqrt(stringToDouble(result.getText( )));
result.setText(Double.toString(answer));
operand.setText("");
}
}
else if (actionCommand.equals("Abs"))
{
answer = Math.abs(stringToDouble(result.getText( )));
result.setText(Double.toString(answer));
operand.setText("");
}
else if (actionCommand.equals("Exp"))
{
answer = Math.pow(stringToDouble(result.getText( )),stringToDouble(operand.getText( )));
result.setText(Double.toString(answer));
operand.setText("");
}
else if (actionCommand.equals("Reset"))
{
answer = 0.0;
result.setText("");
operand.setText("");
}
else if (actionCommand.equals("Clear"))
{
operand.setText("");
}
else
result.setText("Unexpected error.");
}
//Throws NumberFormatException.
private static double stringToDouble(String stringObject)
{
return Double.parseDouble(stringObject.trim( ));
}
//Divide by Zero Exception Class
public class DivideByZeroException extends Exception {
DivideByZeroException() {
}
}
}
答案 0 :(得分：2)
您永远不会将MainPanel添加到applet本身。
即，
add(MainPanel);
此外，由于MainPanel使用BorderLayout，您需要添加一个BorderLayout.XXX常量的子面板。即，
改变这个：
MainPanel.add(buttonPanel);
MainPanel.add(calcPanel);
MainPanel.add(textPanel);
为：
MainPanel.add(buttonPanel, BorderLayout.CENTER);
MainPanel.add(calcPanel, BorderLayout.PAGE_END); // wherever you want to add this
MainPanel.add(textPanel, BorderLayout.PAGE_START);
请注意，使用数组或列表可以大大简化您的代码。
或者可以通过其他方式简化它，例如：
public void assumingCorrectNumberFormats(ActionEvent e)
throws DivideByZeroException {
String actionCommand = e.getActionCommand();
String numbers = "1234567890";
if (numbers.contains(actionCommand)) {
operand.append(actionCommand);
// if you need to work with it as a number
int num = Integer.parseInt(actionCommand);
}
我自己，我使用不同的ActionListener来实现不同的功能，例如一个ActionListener用于数字和.输入按钮，另一个用于操作按钮。