问题参夹在代码中.....package v1ch9.Calculator;
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;
// add the display display = new JButton("0");
display.setEnabled(false);
add(display, BorderLayout.NORTH);
ActionListener insert = new InsertAction();
ActionListener command = new CommandAction(); // add the buttons in a 4 x 4 grid 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("=", command);
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;
}
}
}
//下面这个方法计算用来计算..我试了一下,输入数字后,再按一下+-*/其中一个命令键,就会把输入的数字改为DOUBLE类型后显示,问题是好象
RESULT 被初始化为0, 所以result(+-*/)=x这样的式子得出的结果显示不应该是原数吧???但在计算器上的是正确的...
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;
//JButton 定义的不是一个按键吗??怎么显示在计算器上的不是??高手帮分析下原理
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;
}
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;
// add the display display = new JButton("0");
display.setEnabled(false);
add(display, BorderLayout.NORTH);
ActionListener insert = new InsertAction();
ActionListener command = new CommandAction(); // add the buttons in a 4 x 4 grid 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("=", command);
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;
}
}
}
//下面这个方法计算用来计算..我试了一下,输入数字后,再按一下+-*/其中一个命令键,就会把输入的数字改为DOUBLE类型后显示,问题是好象
RESULT 被初始化为0, 所以result(+-*/)=x这样的式子得出的结果显示不应该是原数吧???但在计算器上的是正确的...
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;
//JButton 定义的不是一个按键吗??怎么显示在计算器上的不是??高手帮分析下原理
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;
}
表达式相当于result = result +-*/ x 这样子得到的结果怎么会是原数呢?
JButton 定义的不是一个按键吗??怎么显示在计算器上的不是??//
display是一个JButton.本来按键显示的时候应该是浅蓝色的,
然后在你的程序中用 display.setEnabled(false); 把按键给禁用了,看起来就是灰色的。
LZ把这句给注释掉再看下结果
表达式相当于result = result +-*/ x 这样子得到的结果怎么会是原数呢?
....................................................................................................................LS的朋友,我的疑问就在于此啊...因为不可能是原数...而显示的时候是以原数输出的,我想知道怎么是这样??
比如:3 + 6 = 9.0。在你的程序中不是显示9.0的吗?这样子得到的结果怎么会象LZ说的“显示的时候是以原数输出的”
当按下+后,会调用CommandAction 的actionPerformed。执行command=event.getActionCommand(); 此时,command为“+”,接着,由于此时的start为false,所以执行else语块,
calculate(Double.parseDouble(display.getText())); 即执行calculate(3.0);调用calculate方法,
由于初始化的时候lastCommand = "= "; 所以执行的是 (lastCommand.equals( "= ")) result = x; 即初始化result的值为3.0,接着再执行
lastCommand = command; 即command的值为“+”
tart = true; 再次把start设为true其它的省略,LZ要弄清的是lastCommand的初始值是lastCommand = "= ";