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

public class KeyPad1 extends Panel
{
   TextField display;		// Readout
   Panel keys;			// Key Pad

   int maxLength = 20;		// Max length of Readout
   String output = "0";		// String to be displayed in
				//    the readout

   boolean decimal = false;	// Has the user inserted a decimal
				//   into the display, yet? (Only
				//   one allowed in a valid number)

   float result=0.0f;		// Result of calc.
   String function="";		// Function currently being performed
   boolean newNumber = true;	// Ready to start a new number?
   boolean finished = false;	// Finished with current calc. ?
				//   (When "=" key pressed)


   boolean memory = false;	// Is there a number in memory?
   float memoryValue = 0.0f;	// Value being held in memory

   public KeyPad1()
   {
      setLayout( new BorderLayout() );
      setFont( new Font("Helvetica", Font.PLAIN, 12) );
      setBackground(Color.lightGray);

      display = new TextField(maxLength+1);
      display.setEditable(false);
      display.setFont( new Font("Helvetica", Font.PLAIN, 12) );
      display.setBackground(Color.white);

      keys = new Panel();
      keys.setLayout( new GridLayout(5,5) );
      keys.setFont( new Font("Helvetica", Font.PLAIN, 12) );
      keys.setBackground(Color.lightGray);

         keys.add( new Button("+/-") );
         keys.add( new Button("") );
         keys.add( new Button("") );
         keys.add( new Button("") );
         keys.add( new Button("AC") );

         keys.add( new Button("M+") );
         keys.add( new Button("7") );
         keys.add( new Button("8") );
         keys.add( new Button("9") );
         keys.add( new Button("/") );

         keys.add( new Button("M-") );
         keys.add( new Button("4") );
         keys.add( new Button("5") );
         keys.add( new Button("6") );
         keys.add( new Button("x") );

         keys.add( new Button("MR") );
         keys.add( new Button("1") );
         keys.add( new Button("2") );
         keys.add( new Button("3") );
         keys.add( new Button("-") );

         keys.add( new Button("MC") );
         keys.add( new Button("0") );
         keys.add( new Button(".") );
         keys.add( new Button("=") );
         keys.add( new Button("+") );

      add("North", display);		// Readout
      add("Center", new Label(""));	// Blank Space 
      add("South", keys);		// Number Pad

      display.resize( display.preferredSize() );
      keys.resize( keys.preferredSize() );

      updateDisplay();			// Call my display function

      show();
   } // End init()

   public void updateDisplay()
   {
      String output_right = "";		// Right Justify the Readout

      for(int i=1; i<=(maxLength-output.length()); i++)
      {
         if ((i==1) && (memory))
            output_right = output_right + "M";
         else
            output_right = output_right + "_";

      }

      output_right = output_right + output;
      display.setText(output_right);
   } // End updateDisplay

   public void appendDigit(String new_d)
   {
      if (output == "0")		// If numbers are added, we don't 
         output = "";			//   want to maintain the leading 0

      if (output.length() < maxLength)
      {
         if (newNumber)			// If starting a new number
         {
            output = new_d;		//    Make this the first digit
            newNumber = false;		//    (then it is no longer new)
         }
         else
            output = output + new_d;	// Else just add another

         updateDisplay();		// Print display, right justified
      }

      if (finished || function == "")	// If the last calculation was finished, then by
      {					//   entering a new digit, we have started a new
					//   calculation
         result = Float.valueOf(output).floatValue();
         finished = false;
         function = "";
      }
   } // End appendDigit()

   public void key_equals()
   {
      evaluate();

      function = "";			// Reset for a new number
      newNumber = true;
      decimal = false;
      finished = true;
   } // End =

   public void evaluate()
   {					// Perform current function
      if (function == "plus")
         result += Float.valueOf(output).floatValue();
      else
      if (function == "minus")
         result -= Float.valueOf(output).floatValue();
      else
      if (function == "times")
         result *= Float.valueOf(output).floatValue();
      else
      if (function == "div")
         result /= Float.valueOf(output).floatValue();
      else
         result = Float.valueOf(output).floatValue();

					// If "=" pressed, setting finished to "true," and we 
      if (finished == true)		// then receive another function key press, we should
         finished = false;		// continue working our last result

					// And reset for a new number
      output = Float.toString(result);
      updateDisplay();

      newNumber = true;
      decimal = false;
   } // End evaluate()

   public boolean handleEvent(Event evt)
   {
      if (evt.arg == "AC")
      {
         result = 0;
         output = Float.toString(result);

         function = "";			// Reset for a new number/function
         newNumber = true;
         decimal = false;
         finished = true;

         updateDisplay();
      }

      if (evt.arg == "+/-")
      {					// Flip sign of displayed number
         float val = Float.valueOf(output).floatValue();
         val *= -1;
         output = Float.toString(val);
         updateDisplay();
      }

      if (evt.arg == "1")   appendDigit("1");
      if (evt.arg == "2")   appendDigit("2");
      if (evt.arg == "3")   appendDigit("3");
      if (evt.arg == "4")   appendDigit("4");
      if (evt.arg == "5")   appendDigit("5");
      if (evt.arg == "6")   appendDigit("6");
      if (evt.arg == "7")   appendDigit("7");
      if (evt.arg == "8")   appendDigit("8");
      if (evt.arg == "9")   appendDigit("9");
      if (evt.arg == "0")
         if (output.length() != 0)   appendDigit("0");

      if (evt.arg == ".")
         if (output.length() < maxLength) 
            if (!decimal)
            {
               decimal = true;
               if (output.length() == 0 || newNumber)
               {
                  output = "0.";
                  newNumber = false;
               }
               else
                  output = output + ".";

               updateDisplay();		// Print display, right justified
            }

      if (evt.arg == "=")		// Evaluate and print results
         key_equals();

      if (evt.arg == "+")
      {
         evaluate();			// Clean up last calculation
         function = "plus";		// and set up for new one
      }

      if (evt.arg == "-")
      {
         evaluate();			// Clean up last calculation
         function = "minus";		// and set up new one
      }

      if (evt.arg == "x")
      {
         evaluate();			// Clean up last calculation
         function = "times";		// and set up new one
      }

      if (evt.arg == "/")
      {
         evaluate();			// Clean up last calculation
         function = "div";		// and set up new one
      }

      if (evt.arg == "M+")
      {
         memory = true;			// Flag our memory value
         key_equals();			// Update result as if "=" has been pressed
					//   and store the result in memory
         memoryValue += Float.valueOf(output).floatValue();
         updateDisplay();
      }

      if (evt.arg == "M-")
      {
         memory = true;			// Flag our memory value
         key_equals();			// Update result as if "=" has been pressed
					//   and store the result in memory
         memoryValue -= Float.valueOf(output).floatValue();
         updateDisplay();
      }

      if (evt.arg == "MR")
      {
         if (memory)
         {
            output = Float.toString(memoryValue);
            updateDisplay();
         }
      }

      if (evt.arg == "MC")
      {
         memory = false;
         memoryValue = 0.0f;
         updateDisplay();
      }

      if (output == "")		// If no numbers are added, we can
         output = "0";		//   replace the lone 0

      return false;
   } // End handleEvent

} // Applet