AWT를 이용한 간단한 - 계산기 -

import java.awt.Frame;
import java.awt.TextField;
import java.awt.Button;
import java.awt.Panel;
import java.awt.GridLayout;
import java.awt.Panel;
import java.awt.Color;
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
import java.awt.event.WindowListener;
import java.awt.event.WindowEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class Calculator extends Frame implements WindowListener, ActionListener{
 TextField result;
 Button[] button;
 boolean num_state = true;
 boolean operator_state=true;
 String op_temp;
 String num_temp;

 public void init() {
  result = new TextField("0", 30);
  result.setEditable(false);
  String[] buttonTitle = {"7", "8", "9", "/",
             "4", "5", "6", "*",
             "1", "2", "3", "-",
             "C", "0", "=", "+"};
  button = new Button[16];
  Panel p = new Panel();

  p.setLayout(new GridLayout(4,4,3,3));

  for (int i=0; i<button.length; i++ ) {
   button[i] = new Button(buttonTitle[i]);
   button[i].setBackground(new Color(58, 226, 206));
   p.add(button[i]);
   button[i].addActionListener(this);
  } //for

  this.add("North", result);
  this.add("Center", p);
  this.setTitle("Calculator");
  this.setBounds(600,300,200,200);
  this.setVisible(true);
  this.addWindowListener(this);
 }//init()
 
 public void windowActivated(WindowEvent e) { }
 public void windowClosed(WindowEvent e) { }
 public void windowClosing(WindowEvent e) {
  System.exit(0);
 }
 public void windowDeactivated(WindowEvent e) { }
 public void windowDeiconified(WindowEvent e) { }
 public void windowIconified(WindowEvent e) { }
 public void windowOpened(WindowEvent e) { }
 
 public void actionPerformed(ActionEvent e) {
  String in = e.getActionCommand();

  if(in.equals("C")){
   result.setText("0");
   num_state = true;
  }else if('0' <= in.charAt(0) && in.charAt(0) <= '9') {
   if (num_state)
    result.setText(in);
   else
    result.setText(result.getText() +in);
   num_state = false;
  }

   if(in.equals("/") || in.equals("*") || in.equals("-") || in.equals("+")) {
    num_temp = result.getText();
    op_temp = in;
    num_state=true;
   }else if(in.equals("=")) {
    if(operator_state) {
     double num1 = Double.parseDouble(num_temp);
     double num2 = Double.parseDouble(result.getText());

     if(op_temp.equals("+")) {
      result.setText("" + (num1+num2));
     }else if(op_temp.equals("-")) {
      result.setText("" + (num1-num2));
     }else if(op_temp.equals("*")) {
      result.setText("" + (num1*num2));
     }else if(op_temp.equals("/")) {
      result.setText("" + (num1/num2));
     }
    }
   }
 }

 public static void main(String[] args) {
  Calculator ct = new Calculator();
  ct.init();
  }
 }