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168 lines (146 loc) · 4.05 KB
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package webstart;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
/**
A panel with calculator buttons and a result display.
*/
public class CalculatorPanel extends JPanel
{
private JTextArea display;
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;
/**
Lays out the panel.
*/
public CalculatorPanel()
{
setLayout(new BorderLayout());
result = 0;
lastCommand = "=";
start = true;
// add the display
display = new JTextArea(10, 20);
add(new JScrollPane(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);
}
/**
Gets the history text.
@return the calculator history
*/
public String getText()
{
return display.getText();
}
/**
Appends a string to the history text.
@param s the string to append
*/
public void append(String s)
{
display.append(s);
}
/**
Adds a button to the center panel.
@param label the button label
@param listener the button listener
*/
private void addButton(String label, ActionListener listener)
{
JButton button = new JButton(label);
button.addActionListener(listener);
panel.add(button);
}
/**
This action inserts the button action string to the
end of the display text.
*/
private class InsertAction implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
String input = event.getActionCommand();
start = false;
display.append(input);
}
}
/**
This action executes the command that the button
action string denotes.
*/
private class CommandAction implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
String command = event.getActionCommand();
if (start)
{
if (command.equals("-"))
{
display.append(command);
start = false;
}
else
lastCommand = command;
}
else
{
try
{
int lines = display.getLineCount();
int lineStart = display.getLineStartOffset(lines - 1);
int lineEnd = display.getLineEndOffset(lines - 1);
String value = display.getText(lineStart, lineEnd - lineStart);
display.append(" ");
display.append(command);
calculate(Double.parseDouble(value));
if (command.equals("="))
display.append("\n" + result);
lastCommand = command;
display.append("\n");
start = true;
}
catch (BadLocationException e)
{
e.printStackTrace();
}
}
}
}
/**
Carries out the pending calculation.
@param x the value to be accumulated with the prior result.
*/
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;
}
}