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Calculator.java
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/*
* Author: Havard Rast Blok
* E-mail: 
* Web : www.rememberjava.com
*/
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/*
* A simple calculator.
*/
public class Calculator extends JFrame implements ActionListener
{
// arithmetic variables
private char savedAction;
private boolean clear;
private float savedValue;
// GUI variables
private JTextField display;
private JPanel buttonsPanel;
private JButton buttons[];
public Calculator()
{
setupGUI();
//set to 'true' to delete display at start
clear = true;
}
private void setupGUI()
{
// add panels and layouts
Container c = getContentPane();
c.setLayout( new BorderLayout() );
display = new JTextField("0");
display.setHorizontalAlignment(JTextField.TRAILING);
c.add(display, BorderLayout.NORTH);
buttonsPanel = new JPanel();
buttonsPanel.setLayout( new GridLayout(4,4) );
c.add( buttonsPanel, BorderLayout.CENTER );
buttons = new JButton[16];
// make the buttons, set ActionListener and add to panel
for(int i=0; i<buttons.length; i++)
{
buttons[i] = new JButton();
buttons[i].addActionListener( this );
buttonsPanel.add( buttons[i] );
}
// set the number captions
buttons[0].setText("7");
buttons[1].setText("8");
buttons[2].setText("9");
buttons[4].setText("4");
buttons[5].setText("5");
buttons[6].setText("6");
buttons[8].setText("1");
buttons[9].setText("2");
buttons[10].setText("3");
buttons[12].setText("0");
// set other captions
buttons[3].setText("/");
buttons[7].setText("*");
buttons[11].setText("-");
buttons[15].setText("+");
buttons[13].setText(".");
buttons[14].setText("=");
pack();
}
public void actionPerformed( ActionEvent e )
{
String str;
char cmd;
// get caption from button and convert to char
str = e.getActionCommand();
cmd = (str.toCharArray())[0];
// display or calulate
if( Character.isDigit( cmd ) || cmd == '.' )
{
if( clear )
{
// save current value and clear the display
savedValue = Float.parseFloat( display.getText() );
display.setText("");
clear = false;
}
// add new digit to display
display.setText( display.getText() + cmd );
}
else
{
calculate(cmd);
}
}
private void calculate(char cmd)
{
float curValue;
float newValue = 0;
// get current value of display
curValue = Float.parseFloat( display.getText() );
if( savedAction == 0 )
{
// if no previous action was save, save this one and clear
clear = true;
savedAction = cmd;
}
else
{
// perform the previous action
switch(savedAction)
{
case '/':
newValue = savedValue / curValue;
break;
case '*':
newValue = savedValue * curValue;
break;
case '-':
newValue = savedValue - curValue;
break;
case '+':
newValue = savedValue + curValue;
break;
}
// display the result and order to clear
display.setText(""+newValue);
clear = true;
if( cmd == '=' )
{
//do not save = action
savedAction = 0;
}
else
{
// save other actions
savedAction = cmd;
}
}
}
public static void main(String args[])
{
new Calculator().show();
}
}
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