import java.awt.*;
import java.applet.*;

public class Calculator extends Applet
{
  private TextField tfAnswer;
  private Button b0,b1,b2,b3,b4,b5,b6,b7,b8,b9;
  private Button bPoint,bEqual,bPlus,bMinus,bClear,bMulti,bDivision;
  
  private String OperatorCurrent,OperatorPre;
  private String ForeScreen,BackScreen;
  private boolean isFloat = false;
  
  public void init()
  {
    OperatorCurrent = new String("");
    OperatorPre = new String("");
    ForeScreen = new String("");
    BackScreen = new String("");
    this.setBackground(Color.gray);
    this.setForeground(Color.blue);
    
    setLayout(null);
    tfAnswer = new TextField();
    tfAnswer.setBounds(5,5,100,20);
    this.add(tfAnswer);
    
    bClear = new Button("C");
    bClear.setBounds(5,30,20,20);
    bClear.setBackground(Color.pink);
    this.add(bClear);
    bDivision = new Button("/");
    bDivision.setBounds(30,30,20,20);
    bDivision.setBackground(Color.green);
    this.add(bDivision);
    bMulti = new Button("*");
    bMulti.setBounds(55,30,20,20);
    bMulti.setBackground(Color.green);
    this.add(bMulti);
    bMinus = new Button("-");
    bMinus.setBounds(80,30,20,20);
    bMinus.setBackground(Color.green);
    this.add(bMinus);
    
    b7 = new Button("7");
    b7.setBounds(5,55,20,20);
    this.add(b7);
    b8 = new Button("8");
    b8.setBounds(30,55,20,20);
    this.add(b8);
    b9 = new Button("9");
    b9.setBounds(55,55,20,20);
    this.add(b9);
    
    b4 = new Button("4");
    b4.setBounds(5,80,20,20);
    this.add(b4);
    b5 = new Button("5");
    b5.setBounds(30,80,20,20);
    this.add(b5);
    b6 = new Button("6");
    b6.setBounds(55,80,20,20);
    this.add(b6);
    bPlus = new Button("+");
    bPlus.setBounds(80,55,20,45);
    bPlus.setBackground(Color.green);
    this.add(bPlus);
    
    b1 = new Button("1");
    b1.setBounds(5,105,20,20);
    this.add(b1);
    b2 = new Button("2");
    b2.setBounds(30,105,20,20);
    this.add(b2);
    b3 = new Button("3");
    b3.setBounds(55,105,20,20);
    this.add(b3);
    
    b0 = new Button("0");
    b0.setBounds(5,130,45,20);
    this.add(b0);
    bPoint = new Button(".");
    bPoint.setBounds(55,130,20,20);
    this.add(bPoint);
    bEqual = new Button("=");
    bEqual.setBounds(80,105,20,45);
    bEqual.setBackground(Color.green);
    this.add(bEqual);
    
  }
  
  public boolean action(Event e, Object o)
  {
    String s = new String("");
    if(e.target instanceof Button)
    {
      if((e.target == b0)||(e.target == b1)||(e.target == b2)||
         (e.target == b3)||(e.target == b4)||(e.target == b5)||
         (e.target == b6)||(e.target == b7)||(e.target == b8)||
         (e.target == b9)||(e.target == bPoint))
      {
        if(e.target != bPoint)
        {
          s = (String)o;
          System.out.print(s);
          doForeScreen(s);
        }
        if((e.target == bPoint)&&(!isFloat))
        {
          isFloat = true;
          s = (String)o;
          if(ForeScreen.equals(""))
          {
            ForeScreen += "0.";
            repaint();
          }
          else
          {
            System.out.print(s);
            doForeScreen(s);
          }
        }
      }
      
      if(e.target == bClear)
      {
        doClear();
      }
      
      if((e.target == bMulti)||(e.target == bDivision)||
         (e.target == bPlus)||(e.target == bMinus))
      {
        if(ForeScreen != "")
        {
          OperatorCurrent = ((String)o);
          doOperator();
          System.out.print((String)o);        
        }
        else
        {
          OperatorPre = ((String)o);
        }
      }
      
      if(e.target == bEqual)
      {
        doOperator();
      }
    }
    
    return true;
  }
  
  public void doOperator()
  {
    double dFore,dBack;
    Double d;
    
    if(OperatorPre.equals(""))
    {
      BackScreen = ForeScreen;
      ForeScreen = "";
      tfAnswer.setText(BackScreen);
      repaint();
    }
    else
    {
      dFore = (new Double(ForeScreen)).doubleValue();
      dBack = (new Double(BackScreen)).doubleValue();
      ForeScreen = "";
      BackScreen = tfAnswer.getText();
      
      if(OperatorPre.equals("+"))
      {
        d = new Double((dBack + dFore));
        tfAnswer.setText(d.toString());
        BackScreen = d.toString();
        repaint();
      }
      if(OperatorPre.equals("-"))
      {
        d = new Double((dBack - dFore));
        tfAnswer.setText(d.toString());
        BackScreen = d.toString();
        repaint();
      }
      if(OperatorPre.equals("*"))
      {
        d = new Double((dBack * dFore));
        tfAnswer.setText(d.toString());
        BackScreen = d.toString();
        repaint();
      }
      if(OperatorPre.equals("/"))
      {
        d = new Double((dBack / dFore));
        tfAnswer.setText(d.toString());
        BackScreen = d.toString();
        repaint();
      }
    }
    OperatorPre = OperatorCurrent;
    repaint();
  }
  
  public void paint(Graphics g)
  {
    //tfAnswer.setText(ForeScreen);
  }
  
  public void doForeScreen(String s)
  {
    ForeScreen += s;
    tfAnswer.setText(ForeScreen);
    repaint();
  }
  
  public void doBackScreen(String s)
  {
    BackScreen = ForeScreen;
    ForeScreen = "";
    tfAnswer.setText(ForeScreen);
    repaint();
  }
  
  public void doClear()
  {
    OperatorCurrent = "";
    OperatorPre = "";
    ForeScreen = "";
    BackScreen = "";
    isFloat = false;
    tfAnswer.setText(ForeScreen);
    repaint();
  }

}