程序如下,运行之后不能显示结果,请大家帮忙解决一下
//Calculator.java import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class Calculator
{
public static void main(String[] args)
{
CalculatorFrame frame=new CalculatorFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}class CalculatorFrame extends JFrame
{
public CalculatorFrame()
{
setTitle("Calculator");
CalculatorPanel panel=new CalculatorPanel();
add(panel);
pack();
}
}
class CalculatorPanel extends JPanel
{
public CalculatorPanel()
{
setLayout(new BorderLayout());
result=0;
lastCommand = "=";
start=true;display=new JButton("0");
display.setEnabled(false);
add(display,BorderLayout.NORTH);
ActionListener command=new CommandAction();
ActionListener insert=new InsertAction(); panel=new JPanel();
panel.setLayout(new GridLayout(4,4));addButton("7",insert);
addButton("8",insert);
addButton("9",insert);
addButton("/",command);addButton("4",insert);
addButton("5",insert);
addButton("6",insert);
addButton("*",command);addButton("1",insert);
addButton("2",insert);
addButton("3",insert);
addButton("-",command);addButton("0",insert);
addButton(".",insert);
addButton("=",insert);
addButton("+",command);add(panel,BorderLayout.CENTER);
}private void addButton(String label,ActionListener listener)
{
JButton button=new JButton(label);
button.addActionListener(listener);
panel.add(button);
}private class InsertAction implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
String input=event.getActionCommand();
if(start)
{
display.setText("");
start=false;
}
display.setText(display.getText()+input);
}
}private class CommandAction implements ActionListener
{
public void actionPerformed(ActionEvent event)
{ String command=event.getActionCommand();
if(start)
{
if(command.equals("-"))
{
display.setText(command);
start=false;
}
else
lastCommand=command;
}
else
{
calculate(Double.parseDouble(display.getText()));
lastCommand=command;
start=true;
}
}
}public void calculate(double x)
{
if(lastCommand.equals("+")) result+=x;
else if(lastCommand.equals("-")) result-=x;
else if(lastCommand.equals("*")) result*=x;
else if(lastCommand.equals("/")) result/=x;
else if(lastCommand.equals("=")) result=x;
display.setText(" "+result);
}
private JButton display;
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;
}
//Calculator.java import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class Calculator
{
public static void main(String[] args)
{
CalculatorFrame frame=new CalculatorFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}class CalculatorFrame extends JFrame
{
public CalculatorFrame()
{
setTitle("Calculator");
CalculatorPanel panel=new CalculatorPanel();
add(panel);
pack();
}
}
class CalculatorPanel extends JPanel
{
public CalculatorPanel()
{
setLayout(new BorderLayout());
result=0;
lastCommand = "=";
start=true;display=new JButton("0");
display.setEnabled(false);
add(display,BorderLayout.NORTH);
ActionListener command=new CommandAction();
ActionListener insert=new InsertAction(); panel=new JPanel();
panel.setLayout(new GridLayout(4,4));addButton("7",insert);
addButton("8",insert);
addButton("9",insert);
addButton("/",command);addButton("4",insert);
addButton("5",insert);
addButton("6",insert);
addButton("*",command);addButton("1",insert);
addButton("2",insert);
addButton("3",insert);
addButton("-",command);addButton("0",insert);
addButton(".",insert);
addButton("=",insert);
addButton("+",command);add(panel,BorderLayout.CENTER);
}private void addButton(String label,ActionListener listener)
{
JButton button=new JButton(label);
button.addActionListener(listener);
panel.add(button);
}private class InsertAction implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
String input=event.getActionCommand();
if(start)
{
display.setText("");
start=false;
}
display.setText(display.getText()+input);
}
}private class CommandAction implements ActionListener
{
public void actionPerformed(ActionEvent event)
{ String command=event.getActionCommand();
if(start)
{
if(command.equals("-"))
{
display.setText(command);
start=false;
}
else
lastCommand=command;
}
else
{
calculate(Double.parseDouble(display.getText()));
lastCommand=command;
start=true;
}
}
}public void calculate(double x)
{
if(lastCommand.equals("+")) result+=x;
else if(lastCommand.equals("-")) result-=x;
else if(lastCommand.equals("*")) result*=x;
else if(lastCommand.equals("/")) result/=x;
else if(lastCommand.equals("=")) result=x;
display.setText(" "+result);
}
private JButton display;
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;
}
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abc.java:7: 类 Calculator 是公共的,应在名为 Calculator.java 的文件中声明
public class Calculator
^
1 错误是不是报这个错误?我第一反应是把这个代码放在名为abc.java里运行。 改了名字就OK了。
result = x;还有这里,点 “=” 等号这个操作符时,它会直接返回输入数字,和 “=”等号。 当然算不出结果。