Serial communication between Android and Arduino - cannot receive data correctly

I'm attempting to send a single char command from my Android app to an Arduino Uno R3, and then receive data from a sensor based on which command is read. I've successfully linked my Nexus 7 and the Arduino, the RX blinks when I send the command from the app. However, I have my Arduino code set up to blink the on-board LED 3 times when a valid command is received - this does not occur. The setup works fine when I use a terminal emulator app or Tera Term on my PC, so I'm fairly certain the problem lies within my Java code. The baud rate, data/stop bits, and parity are all set correctly within the app (115200, 8, 1, and none) so I don't see it being an issue with that.

I'm using Felhr's USB Serial library - http://felhr85.net/2014/11/11/usbserial-a-serial-port-driver-library-for-android-v2-0/

Here is the relevant Android code. I know the byte is sending, and when I have the hexInfo editText show the byte, it correctly shows as the ASCII value ([115] for 's', for example).

private double serialUser(char command) {
        mUsbOutput = 0;

        byte commandB[] = new byte[1];
        commandB[0] = (byte) command;

        hexInfo.setText(Arrays.toString(commandB));

        if (command == 's') {
            mSerialPort.write(commandB);
            commandInfo.setText(String.valueOf(command));

        } else if (command=='e' || command=='c' || command=='f') {
            mSerialPort.write(commandB);
            commandInfo.setText(String.valueOf(command));

        } else {
            Toast.makeText(getApplicationContext(), "invalid command", Toast.LENGTH_SHORT).show();
        }            

        return mUsbOutput;
    }

    UsbSerialInterface.UsbReadCallback mCallback = new UsbSerialInterface.UsbReadCallback() {
        @Override
        public void onReceivedData(byte[] arg0) {
            Toast.makeText(getApplicationContext(), "data received", Toast.LENGTH_SHORT).show();

            //String data = new String(arg0);
            //mUsbOutput = Double.valueOf(data);
            //hexInfo.setText(String.valueOf(mUsbOutput));
        }
    };

Here is my Arduino code. I may have set up the Serial portions incorrectly, but I'm not sure.

#include <DistanceSRF04.h>
#include <Encoder.h>
#include <math.h>

#define rxPin 6
#define txPin 7

DistanceSRF04 Dist;
int time, times[10];
float heightFloor, heightCurb;
Encoder myEnc(4, 5);
int led = 13;


void setup()
{  
  Serial.begin(115200);
  Dist.begin(2,3);
  pinMode(led, OUTPUT);
}

const double Pi = 3.14159265359; // 3.141593, set to 1 for testing purposes
double encoderPosition  = -999;
byte incomingByte;
char incomingCommand;

void loop(){

if(Serial.available()>0){
  blinkled();
  incomingByte = (byte) Serial.read();
  incomingCommand = (char) incomingByte;
}

  double newPosition = abs(myEnc.read()); // gets raw data, 1440 ticks = 1 rev
  double revs = newPosition/(double)960; // calculates number of revs
  double diameter = 15; // specify wheel diameter
  double distanceEnc = diameter*Pi*revs; // calculates distance 
  double heightDiff;
  int timesum = 0;

  distanceEnc = round(distanceEnc*1000.0l)/1000.0l; // round distance to 3 decimal places

  if (newPosition != encoderPosition) { // write new position to serial
   encoderPosition = newPosition;     
    //Serial.println(distanceEnc,3);
    //Serial.println(revs,3);
  }
  if (incomingCommand == 's'){
    myEnc.write(0);
    revs = 0;
    blinkled();
  }
  if (incomingCommand == 'e'){  
    Serial.print(distanceEnc); 
    blinkled();      
  }
  if (incomingCommand == 'f'){
    time = Dist.getDistanceTime();
    heightFloor = (float) time/(148.00);  
    blinkled();
  }
  if(incomingCommand =='c'){    
    for(int i=1; i<11; i++){
      times[i] = Dist.getDistanceTime();
      delay(100); 
      timesum = timesum+times[i];
    }
    time = timesum/(int)10;
    heightCurb = (float) time/(148.00);
    heightDiff = heightFloor - heightCurb;     
    Serial.print(heightDiff);  
    blinkled();
  }
}

void blinkled(){ 
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(250);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(250);     
  digitalWrite(led, HIGH); 
  delay(250);             
  digitalWrite(led, LOW);  
  delay(250);     
  digitalWrite(led, HIGH);   
  delay(250);               
  digitalWrite(led, LOW);   
  delay(250);     
}