4x4 Keypad Java

package application;
import java.util.HashMap;

import com.pi4j.io.gpio.GpioController;
import com.pi4j.io.gpio.GpioFactory;
import com.pi4j.io.gpio.GpioPinDigitalInput;
import com.pi4j.io.gpio.GpioPinDigitalOutput;
import com.pi4j.io.gpio.Pin;
import com.pi4j.io.gpio.PinPullResistance;
import com.pi4j.io.gpio.PinState;
import com.pi4j.io.gpio.RaspiPin;
import com.pi4j.io.gpio.event.GpioPinDigitalStateChangeEvent;
import com.pi4j.io.gpio.event.GpioPinListenerDigital;

/**
 * The Class PiezoKeypad.
 */
public class PiezoKeypad
{

   /**
    * <pre>
    * Keypad pin schema key = pina + pinb
    *     (output/input) (column/row)
    * 1 =   4   8
    * 2 =   3   8
    * 3 =   2   8
    * A =   1   8
    * 4 =   4   7
    * 5 =   3   7
    * 6 =   2   7
    * B =   1   7
    * 7 =   4   6
    * 8 =   3   6
    * 9 =   2   6
    * C =   1   6
    * * =   4   5
    * 0 =   3   5
    * # =   2   5
    * D =   1   5
    * </pre>
    *
    * .
    */

   /** The Constant PINMAPPING. */
   private static final HashMap<String, String> PINMAPPING = new HashMap<String, String>();

   /** The gpio. */
   private final GpioController theGpio = GpioFactory.getInstance();

   /** The Constant PIN_1_IN. */
   private static final Pin PIN_1_OUT = RaspiPin.GPIO_01;

   /** The Constant PIN_2_IN. */
   private static final Pin PIN_2_OUT = RaspiPin.GPIO_02;

   /** The Constant PIN_3_IN. */
   private static final Pin PIN_3_OUT = RaspiPin.GPIO_03;

   /** The Constant PIN_4_OUT. */
   private static final Pin PIN_4_OUT = RaspiPin.GPIO_04;

   /** The Constant PIN_5_IN. */
   private static final Pin PIN_5_IN = RaspiPin.GPIO_05;

   /** The Constant PIN_6_IN. */
   private static final Pin PIN_6_IN = RaspiPin.GPIO_06;

   /** The Constant PIN_7_IN. */
   private static final Pin PIN_7_IN = RaspiPin.GPIO_07;

   /** The Constant PIN_8_IN. */
   private static final Pin PIN_8_IN = RaspiPin.GPIO_08;

   /** The pin1. */
   private final GpioPinDigitalOutput thePin1 = theGpio
         .provisionDigitalOutputPin(PIN_1_OUT);

   /** The pin2. */
   private final GpioPinDigitalOutput thePin2 = theGpio
         .provisionDigitalOutputPin(PIN_2_OUT);

   /** The pin3. */
   private final GpioPinDigitalOutput thePin3 = theGpio
         .provisionDigitalOutputPin(PIN_3_OUT);

   /** The pin4. */
   private final GpioPinDigitalOutput thePin4 = theGpio
         .provisionDigitalOutputPin(PIN_4_OUT);

   /** The pin5. */
   private final GpioPinDigitalInput thePin5 = theGpio
         .provisionDigitalInputPin(PIN_5_IN, PinPullResistance.PULL_UP);

   /** The pin6. */
   private final GpioPinDigitalInput thePin6 = theGpio
         .provisionDigitalInputPin(PIN_6_IN, PinPullResistance.PULL_UP);

   /** The pin7. */
   private final GpioPinDigitalInput thePin7 = theGpio
         .provisionDigitalInputPin(PIN_7_IN, PinPullResistance.PULL_UP);

   /** The pin8. */
   private final GpioPinDigitalInput thePin8 = theGpio
         .provisionDigitalInputPin(PIN_8_IN, PinPullResistance.PULL_UP);

   /** The outputs. */
   private final GpioPinDigitalOutput theOutputs[] = { thePin1,
                                                       thePin2,
                                                       thePin3,
                                                       thePin4 };

   /** The input. */
   private GpioPinDigitalInput theInput;

   /** The in id. */
   private int theInId;

   /** The first pin. */
   private int theFirstPin = 0;

   /** The second pin. */
   private int theSecondPin = 0;

   /**
    * Instantiates a new piezo keypad.
    */
   public PiezoKeypad()
   {
      initMapping();

      initListeners();
   }

   /**
    * Check pins.
    *
    * Determins the pressed key based on the activated GPIO pins.
    */
   private synchronized void checkPins()
   {
      if (theFirstPin != 0 && theSecondPin != 0)
      {
         System.out.println("theFirstPin= " + theFirstPin
                          + " theSecondPin= " + theSecondPin);

         System.out.println(PINMAPPING.get(String.valueOf(theFirstPin)
                                         + String.valueOf(theSecondPin)));

         theFirstPin = 0;
         theSecondPin = 0;
      }
   }

   /**
    * Find output.
    *
    * Sets output lines  to high and then to low one by one.
    * Then the input line is tested. If its state is low, we have the right output line and therefore
    * a mapping to a key on the keypad.
    */
   private void findOutput()
   {
      // now test the inputs by setting the outputs from high to low
      // one by one
      for (int myO = 0; myO < theOutputs.length; myO++)
      {
         for (final GpioPinDigitalOutput myTheOutput : theOutputs)
         {
            myTheOutput.high();
         }

         theOutputs[myO].low();

         // input found?
         if (theInput.isLow())
         {
            theSecondPin = theInId;

            if (myO == 0)
            {
               theFirstPin = 1;
            }
            else
            {
               theFirstPin = 4;
            }

            checkPins();
            break;
         }
      }

      for (final GpioPinDigitalOutput myTheOutput : theOutputs)
      {
         myTheOutput.low();
      }
   }

   /**
    * Inits the listeners.
    */
   private void initListeners()
   {
      thePin5.addListener(new GpioPinListenerDigital()
      {
         @Override
         public void handleGpioPinDigitalStateChangeEvent(
               final GpioPinDigitalStateChangeEvent aEvent)
         {
            if (aEvent.getState() == PinState.LOW)
            {
               theInput = thePin5;
               theInId = 5;
               findOutput();
            }
         }
      });
      thePin6.addListener(new GpioPinListenerDigital()
      {
         @Override
         public void handleGpioPinDigitalStateChangeEvent(
               final GpioPinDigitalStateChangeEvent aEvent)
         {
            if (aEvent.getState() == PinState.LOW)
            {
               theInput = thePin6;
               theInId = 6;
               findOutput();
            }
         }
      });
      thePin7.addListener(new GpioPinListenerDigital()
      {
         @Override
         public void handleGpioPinDigitalStateChangeEvent(
               final GpioPinDigitalStateChangeEvent aEvent)
         {
            if (aEvent.getState() == PinState.LOW)
            {
               theInput = thePin7;
               theInId = 7;
               findOutput();
            }
         }
      });
      thePin8.addListener(new GpioPinListenerDigital()
      {
         @Override
         public void handleGpioPinDigitalStateChangeEvent(
               final GpioPinDigitalStateChangeEvent aEvent)
         {
            if (aEvent.getState() == PinState.LOW)
            {
               theInput = thePin8;
               theInId = 8;
               findOutput();
            }
         }
      });
   }

   /**
    * Inits the mapping.
    *
    * Maps input/output line to key on keypad.
    */
   private void initMapping()
   {
      PINMAPPING.put("48", "1");
      PINMAPPING.put("38", "2");
      PINMAPPING.put("28", "3");
      PINMAPPING.put("18", "A");
      PINMAPPING.put("47", "4");
      PINMAPPING.put("37", "5");
      PINMAPPING.put("27", "6");
      PINMAPPING.put("17", "B");
      PINMAPPING.put("46", "7");
      PINMAPPING.put("36", "8");
      PINMAPPING.put("26", "9");
      PINMAPPING.put("16", "C");
      PINMAPPING.put("45", "*");
      PINMAPPING.put("35", "0");
      PINMAPPING.put("25", "#");
      PINMAPPING.put("15", "D");
   }
}