Develop Reference

Reading temperature through DHT11 using Android Things

I am using Raspberry pi3 and DHT11 sensor for temperature monitoring project.
I have following pin positions
VCC to pin no : 2
Ground to pin no : 6
Output to GPIO : BCM22 i.e pin no 15
Code that I have used:
public class WeatherStationActivity extends Activity {
private Handler mHandler = new Handler();
private TextView mTxtStatus;
private PeripheralManagerService service = new PeripheralManagerService();
private Gpio tempGpio;
private int i = 0;
int[] dht11_dat = {0, 0, 0, 0, 0};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d("Weather station", "Started Weather Station");
setContentView(R.layout.activity_main);
mTxtStatus = (TextView) findViewById(R.id.txtStatus);
try {
tempGpio = service.openGpio("BCM22");
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
if (i == 10) {
handler.removeCallbacks(this);
} else {
getTemp();
handler.postDelayed(this, 5000);
}
i++;
}
}, 5000);
} catch (Exception e) {
e.printStackTrace();
}
}
private void getTemp() {
boolean laststate = false;
try {
laststate = tempGpio.getValue();
} catch (IOException e) {
e.printStackTrace();
}
int j = 0;
final int MAXTIMINGS = 85;
dht11_dat[0] = dht11_dat[1] = dht11_dat[2] = dht11_dat[3] = dht11_dat[4] = 0;
try {
tempGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);
// tempGpio.setActiveType(Gpio.ACTIVE_LOW);
tempGpio.setValue(false);
// Thread.sleep(18);
TimeUnit.MILLISECONDS.sleep(18);
// tempGpio.setActiveType(Gpio.ACTIVE_HIGH);
// tempGpio.setActiveType(Gpio.ACTIVE_HIGH);
tempGpio.setValue(true);
TimeUnit.MICROSECONDS.sleep(40);
tempGpio.setDirection(Gpio.DIRECTION_IN);
/* tempGpio.setActiveType(Gpio.ACTIVE_HIGH);
tempGpio.setValue(true);*/
// tempGpio.setValue(true);
StringBuilder value = new StringBuilder();
for (int i = 0; i < MAXTIMINGS; i++) {
int counter = 0;
while (tempGpio.getValue() == laststate) {
counter++;
TimeUnit.MICROSECONDS.sleep(1);
if (counter == 255) {
break;
}
}
laststate = tempGpio.getValue();
mTxtStatus.append("\nLast State of Sensor " + laststate);
if (counter == 255) {
break;
}
//* ignore first 3 transitions *//*
if ((i >= 4) && (i % 2 == 0)) {
//* shove each bit into the storage bytes *//*
dht11_dat[j / 8] <<= 1;
if (counter > 16) {
dht11_dat[j / 8] |= 1;
}
j++;
}
}
// check we read 40 bits (8bit x 5 ) + verify checksum in the last
// byte
if ((j >= 40) && checkParity()) {
value.append(dht11_dat[2]).append(".").append(dht11_dat[3]);
Log.i("Logger", "temperature value readed: " + value.toString());
mTxtStatus.append("\nTemp " + value.toString());
} else {
mTxtStatus.append("\nNothing is working ");
Log.i("Logger", "Nothing is working ");
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (Exception ex) {
ex.printStackTrace();
}
}
private boolean checkParity() {
return dht11_dat[4] == (dht11_dat[0] + dht11_dat[1] + dht11_dat[2] + dht11_dat[3] & 0xFF);
}
}
Above code is giving me "Nothing is working" as output.
Any suggestion where I might be doing wrong?

You can't read data from DHT11 using Raspberry Pi 3 with Android Things because duration of DHT11 response pulses is from 26-28 us to 70 us, but max frequency of RP3 with AT GPIO is around 3kHz, which means around 300 us pulse duration. Take a look at answers to this question.

Why I can't send a large amount of data via Bluetooth Android?

I'm still newbie and I need help to coding my Android Studio >0<
I can't to send a long data, although I change the size of "buffer". What should I do ?
This is the receiver program :
public void run() {
InputStream inputStream;
try {
inputStream = mBTSocket.getInputStream();
while (!bStop) {
byte[] buffer = new byte[1024];
if (inputStream.available() > 0)
{
inputStream.read(buffer);
int i = 0;
/*
* This is needed because new String(buffer) is taking the entire buffer i.e. 256 chars on Android 2.3.4 http://stackoverflow.com/a/8843462/1287554
*/
for (i = 0; i < buffer.length && buffer[i] != 0; i++) {}
final String strInput = new String(buffer, 0, i);
/*
* If checked then receive text, better design would probably be to stop thread if unchecked and free resources, but this is a quick fix
*/
}
Thread.sleep(500);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
This are the sender program :
public void sendStringBT(String s)
{
try {
mBTSocket.getOutputStream().write(s.getBytes());
sleep();
Toast.makeText(getApplicationContext(), "Sent...", Toast.LENGTH_SHORT).show();
mBTSocket.getOutputStream().flush();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
This is how to we call to send data :
sendStringBT(dataPage6); //send data via Bluetooth

I think the problem is in the design of the receiver (using Sleep in an endless cycle ...) I Solved BTL communication in .net Xamarin, but the principle should be the same.
Reading from btlInputStream must be quick and can not use sleep. You use an endless cycle, reading in buffer (OK). Immediately a dune bytes to an auxiliary large buffer (use read / write cursor) and then, for example, in timer treat the data (I suppose you are using some packet protocol)
while (ContinueCycle)
{
int rxlen;
lock (InternalBufferReadLock)
{//Pouze rychle prectu a schovam si do pole
rxlen = USBConnection.BulkTransfer(USBEndPointRead, InternalBufferRead, InternalBufferRead.Length, 0);
Array.Copy(InternalBufferRead, TempBufferRead, rxlen);
}
lock (BufferReadLock)
{
for (int i = 2; i < rxlen; i++)
{
BufferRead[BufferReadWriteCursor] = TempBufferRead[i];
BufferReadWriteCursor++;
}
}
}
and in timer save it to MainBuffer from which the data is processing
if (tmpWriteCursor > tmpReadCursor)
{
lock (BufferReadLock)
{
int newBytes = tmpWriteCursor - tmpReadCursor;
for (int i = 0; i < newBytes; i++)
{
BufferReadMain[BufferReadReadCursor] = BufferRead[BufferReadReadCursor++];
}
}
}
...
bool newline = false;
string tmpRadek = "";
int lastLineIndex = 0;
List<string> list = new List<string>();
for (int i = LastWriteLineIndex; i < tmpWriteCursor; i++)
{
if (BufferReadMain[i] >= 32 && BufferReadMain[i] <= 255)
{
tmpRadek += (char)BufferReadMain[i];
}
else if (BufferReadMain[i] == 13) newline = true;
else if (BufferReadMain[i] == 10)
{
if (newline)
{
newline = false;
list.Add(Utils.GetFormatedDateTime(DateTime.Now) + " " + tmpRadek);
tmpRadek = "";
lastLineIndex = i + 1;
}
}
else
{
tmpRadek += "?" + BufferReadMain[i].ToString() + "?";
}
}

How to do fractions in an Android editText. Inputfilter? Custom IME?

I'm trying to write code for an editText which can accept imperial values { ie. 1 , 3/4 , 1 1/3}. So far, with a lot of help from StackOverflow, I have it just about nailed. But there are three things missing.
android:inputType="number" or numberSigned, numberDecimal, phone etc
none of these display the / key I need to enter data and the QWERTY keyboard is too cumbersome for a single keypress. I'm amazed there isn't a keyboard for this, what do the yanks do? Can I override and replace a single key on the stock keyboard, do I have to implement my own keyboard for this seemingly simple task?
I am also struggling with the logic which prevents the first character being a space or /. I can allow one of each in a given string no problem, I just can't prevent it being the first key. Additionally, when you enter a value - like "1 5/9" - if you backspace to the /, the flags are not reset, so you are prohibited from entering another /.
Code for the InputFilter is as follows:
imperial_filter = new InputFilter() {
boolean canEnterSpace = true, canEnterSlash = true;
public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
if (imperial_editText.getText().toString().equals("")) {
canEnterSpace = true;
canEnterSlash = true;
}
StringBuilder builder = new StringBuilder();
for (int i = start; i < end; i++) {
char currentChar = source.charAt(i);
if (Character.isDigit(currentChar) || (Character.isWhitespace(currentChar) && canEnterSpace && canEnterSlash) || (currentChar == '/' && canEnterSlash)) {
builder.append(currentChar);
if (Character.isWhitespace(currentChar)) canEnterSpace = false;
if (currentChar == '/') canEnterSlash = false;
}
}
return builder.toString();
}
};
And this one is a little more complex, slightly adapted from code already on StackOverflow:
public float testImperialString(String testString) {
boolean goodInput = true, goodInputSpace = true, containsSpace = false;
float result = 0, whole = 0;
String fractions = "";
if (testString.contains(" ")) {
containsSpace = true;
String pieces[] = testString.split(" ");
try {
whole = Float.parseFloat(pieces[0]);
fractions = pieces[1];
} catch (Exception e) {
goodInputSpace = false;
}
} else fractions = testString;
if (fractions.contains("/")) {
//possible division
String pieces[] = fractions.split("/");
if (pieces.length != 2) {
goodInput = false;
} else {
try {
float numerator = Float.parseFloat(pieces[0]);
float denominator = Float.parseFloat(pieces[1]);
result = numerator / denominator;
} catch (Exception e) {
goodInput = false;
}
}
}
if (!testString.contains(" ") && !(result > 0)) {
try {
result = Float.parseFloat(testString);
} catch (Exception e) {
goodInput = false;
}
}
Log.d(TAG, "Contains Space = " + containsSpace + " Good Input = " + goodInput + " Good InputSpace = " + goodInputSpace);
return whole + result;
}
I run that result through a method which converts imperial measurements into a metric equivalent, that I can perform maths functions with.
TL:DR
I need a number keyboard with a / symbol
I need to prevent a space or / as the first letter of an input
I need to re-allow a space or / input, if a previous occurrence in a string was deleted.

Android: Loading large txt file(120k lines) from raw folder has delay the first time

I am using an AsyncTask to parse a very large txt file in my application and i noticed something weird: The first time this AsyncTask is called it takes very long time to finish(10-20 seconds) and the next times it's almost instantly.
So i am guessing i should somehow load the txt file into memory when the app starts and go from there.
Is there any ways to do this or is this the right thing to do in the first place?
Should some kind of cache implementation solve my problem?
Would it be a good idea to use the Android Cache system?
This is my AsyncTask for referece:
public class AnalyzeReviewsAsync extends AsyncTask<ArrayList<Place.Review>, String, String> {
private final Activity activity;
private ProgressDialog progressDialog;
private SinglePlaceCallbacks callbacks;
public AnalyzeReviewsAsync(Activity activity, SinglePlaceCallbacks callbacks) {
this.activity = activity;
this.callbacks = callbacks;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
progressDialog = new ProgressDialog(activity);
progressDialog.setMessage("Analyzing...");
progressDialog.show();
}
#Override
protected String doInBackground(ArrayList<Place.Review>... params) {
try {
return parseReviews(params[0]);
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
progressDialog.dismiss();
String review = s == null ? "Not present" : s;
callbacks.setReviewsTxt(review);
}
private String parseReviews(ArrayList<Place.Review> reviewArrayList) throws IOException {
if(reviewArrayList!=null && reviewArrayList.size()>0) {
String reviewOutput = "";
for (Place.Review r : reviewArrayList) {
reviewOutput += "<p> <font color='" + getReviewColor(SentiWordNet.getInstance().analyzeReview(r.text)) + "'>";
reviewOutput += r.text;
reviewOutput += "</font></p>";
}
return reviewOutput;
}else{
return null;
}
}
private String getReviewColor(String review) {
if (review.equals("very positive")) {
//return Constants.getContext().getResources().getString(R.color.very_positive);
return "lime";
} else if (review.equals("positive")) {
//return Constants.getContext().getResources().getString(R.color.positive);
return "teal";
} else if (review.equals("negative")) {
//return Constants.getContext().getResources().getString(R.color.negative);
return "maroon";
} else if (review.equals("very negative")) {
//return Constants.getContext().getResources().getString(R.color.very_negative);
return "red";
} else {
//return Constants.getContext().getResources().getString(R.color.neutral);
return "grey";
}
}
}
Nothing fails the first time, so it is nothing different in code, here is my SentiWordNet class for referece:
public class SentiWordNet {
private Map<String, Double> dictionary;
private static SentiWordNet _instance = null;
private SentiWordNet(Context context) throws IOException {
// This is our main dictionary representation
dictionary = new HashMap<String, Double>();
// From String to list of doubles.
HashMap<String, HashMap<Integer, Double>> tempDictionary = new HashMap<String, HashMap<Integer, Double>>();
InputStream rawRes = context.getResources().openRawResource(R.raw.swn);
BufferedReader csv = null;
try {
csv = new BufferedReader(new InputStreamReader(rawRes, "UTF8"));
int lineNumber = 0;
String line;
while ((line = csv.readLine()) != null) {
lineNumber++;
// If it's a comment, skip this line.
if (!line.trim().startsWith("#")) {
// We use tab separation
String[] data = line.split("\t");
String wordTypeMarker = data[0];
// Example line:
// POS ID PosS NegS SynsetTerm#sensenumber Desc
// a 00009618 0.5 0.25 spartan#4 austere#3 ascetical#2
// ascetic#2 practicing great self-denial;...etc
// Is it a valid line? Otherwise, through exception.
if (data.length != 6) {
throw new IllegalArgumentException(
"Incorrect tabulation format in file, line: "
+ lineNumber
);
}
// Calculate synset score as score = PosS - NegS
Double synsetScore = Double.parseDouble(data[2])
- Double.parseDouble(data[3]);
// Get all Synset terms
String[] synTermsSplit = data[4].split(" ");
// Go through all terms of current synset.
for (String synTermSplit : synTermsSplit) {
// Get synterm and synterm rank
String[] synTermAndRank = synTermSplit.split("#");
String synTerm = synTermAndRank[0] + "#"
+ wordTypeMarker;
int synTermRank = Integer.parseInt(synTermAndRank[1]);
// What we get here is a map of the type:
// term -> {score of synset#1, score of synset#2...}
// Add map to term if it doesn't have one
if (!tempDictionary.containsKey(synTerm)) {
tempDictionary.put(synTerm,
new HashMap<Integer, Double>());
}
// Add synset link to synterm
tempDictionary.get(synTerm).put(synTermRank,
synsetScore);
}
}
}
// Go through all the terms.
for (Map.Entry<String, HashMap<Integer, Double>> entry : tempDictionary
.entrySet()) {
String word = entry.getKey();
Map<Integer, Double> synSetScoreMap = entry.getValue();
// Calculate weighted average. Weigh the synsets according to
// their rank.
// Score= 1/2*first + 1/3*second + 1/4*third ..... etc.
// Sum = 1/1 + 1/2 + 1/3 ...
double score = 0.0;
double sum = 0.0;
for (Map.Entry<Integer, Double> setScore : synSetScoreMap
.entrySet()) {
score += setScore.getValue() / (double) setScore.getKey();
sum += 1.0 / (double) setScore.getKey();
}
score /= sum;
dictionary.put(word, score);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (csv != null) {
csv.close();
}
}
}
public static SentiWordNet getInstance() throws IOException {
if (_instance == null) {
_instance = new SentiWordNet(Constants.getContext());
}
return _instance;
}
public Double extract(String word) {
Double total = (double) 0;
if (dictionary.get(word + "#n") != null) {
total = dictionary.get(word + "#n") + total;
}
if (dictionary.get(word + "#a") != null) {
total = dictionary.get(word + "#a") + total;
}
if (dictionary.get(word + "#r") != null) {
total = dictionary.get(word + "#r") + total;
}
if (dictionary.get(word + "#v") != null) {
total = dictionary.get(word + "#v") + total;
}
return total;
}
public String analyzeReview(String review) {
String[] words = review.split("\\s+");
double totalScore = 0, averageScore;
for (String word : words) {
word = word.replaceAll("([^a-zA-Z\\s])", "");
if (_instance.extract(word) == null) {
continue;
}
Log.d("Total Score", String.valueOf(totalScore));
totalScore += _instance.extract(word);
}
averageScore = totalScore;
if (averageScore >= 0.75) {
return "very positive";
} else if (averageScore > 0.25 && averageScore < 0.5) {
return "positive";
} else if (averageScore >= 0.5) {
return "positive";
} else if (averageScore < 0 && averageScore >= -0.25) {
return "negative";
} else if (averageScore < -0.25 && averageScore >= -0.5) {
return "negative";
} else if (averageScore <= -0.75) {
return "very negative";
}
return "neutral";
}

Compare contents of two files line by line

public class MainActivity extends Activity {
FileOutputStream fos;
FileInputStream fOne, fTwo;
ArrayList<String> arr1 = new ArrayList<String>();
ArrayList<String> arr2 = new ArrayList<String>();
ArrayList<String> words = new ArrayList<String>();
ArrayList<String> wordsTwo = new ArrayList<String>();
int count = 0;
int countTwo = 0;
int countThree = 0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button fileOne = (Button)findViewById(R.id.file1);
Button fileTwo = (Button)findViewById(R.id.file2);
Button compare = (Button)findViewById(R.id.compare);
arr1.add("1");
arr1.add("2");
arr1.add("3");
arr1.add("4");
//arr1.add("3");
arr2.add("1");
arr2.add("2");
fileOne.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
try
{
fos = openFileOutput("File1", Context.MODE_PRIVATE);
for(int temp = 0; temp< arr1.size(); temp++)
{
fos.write((arr1.get(temp).getBytes()) );
fos.write(System.getProperty("line.separator").getBytes());
}
fos.close();
fos.flush();
}
catch(Exception e)
{
}
}
});
fileTwo.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
try
{
fos = openFileOutput("File2", Context.MODE_PRIVATE);
for(int temp = 0; temp< arr2.size(); temp++)
{
fos.write((arr2.get(temp).getBytes()) );
fos.write(System.getProperty("line.separator").getBytes());
}
fos.close();
fos.flush();
}
catch(Exception e)
{
}
}
});
compare.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
try
{
fOne = openFileInput("File1");
fTwo = openFileInput("File2");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Scanner scanFile = new Scanner(new DataInputStream(fOne));
Scanner scanFileT = new Scanner(new DataInputStream(fTwo));
words = new ArrayList<String>();
wordsTwo = new ArrayList<String>();
while (scanFile.hasNextLine())
{
if(scanFile.nextLine()!=null)
{
count++;
}
while(scanFileT.hasNextLine())
{
if(scanFileT.nextLine()!=null)
{
countTwo++;
}
}
}
try
{
fOne.close();
fTwo.close();
scanFile.close();
scanFileT.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "One : " + count, 1000).show();
Toast.makeText(getBaseContext(), "Two : " + countTwo, 1000).show();
Toast.makeText(getBaseContext(), "Three : " + countThree, 1000).show();
count = 0 ;
countTwo = 0;
countThree = 0;
}
});
}
}
Above is the code to write and read the file. What I did here, write two files and read the contents..Now I have to compare contents of files line by line. What needs to be done?

Try following code. This will give you desired output. I took files from asset directory. So you need to replace that line of code if you are taking files from other directory.
private void compareFiles() throws Exception {
String s1 = "";
String s2 = "", s3 = "", s4 = "";
String y = "", z = "";
// Reading the contents of the files
BufferedReader br = new BufferedReader(new InputStreamReader(
getAssets().open("first.txt")));
BufferedReader br1 = new BufferedReader(new InputStreamReader(
getAssets().open("second.txt")));
while ((z = br1.readLine()) != null) {
s3 += z;
s3 += System.getProperty("line.separator");
}
while ((y = br.readLine()) != null) {
s1 += y;
s1 += System.getProperty("line.separator");
}
// String tokenizing
StringTokenizer st = new StringTokenizer(s1);
String[] a = new String[10000];
for (int l = 0; l < 10000; l++) {
a[l] = "";
}
int i = 0;
while (st.hasMoreTokens()) {
s2 = st.nextToken();
a[i] = s2;
i++;
}
StringTokenizer st1 = new StringTokenizer(s3);
String[] b = new String[10000];
for (int k = 0; k < 10000; k++) {
b[k] = "";
}
int j = 0;
while (st1.hasMoreTokens()) {
s4 = st1.nextToken();
b[j] = s4;
j++;
}
// comparing the contents of the files and printing the differences, if
// any.
int x = 0;
for (int m = 0; m < a.length; m++) {
if (a[m].equals(b[m])) {
} else {
x++;
Log.d("Home", a[m] + " -- " + b[m]);
}
}
Log.d("Home", "No. of differences : " + x);
if (x > 0) {
Log.d("Home", "Files are not equal");
} else {
Log.d("Home", "Files are equal. No difference found");
}
}
Input File 1
Hi
Hello
Chintan
Rathod
Input File 2
Hi
HellO
Chintan
RathoD
Output
08-26 12:07:58.219: DEBUG/Home(2350): Hello3. -- HellO3.
08-26 12:07:58.219: DEBUG/Home(2350): Rathod -- RathoD
08-26 12:07:58.229: DEBUG/Home(2350): No. of differences : 2
08-26 12:07:58.229: DEBUG/Home(2350): Files are not equal
Edit
To get Difference between two files
Use StringUtils library which is provide by Apache and check this Documentation for more about that library.
And modify following lines of code.
int x = 0;
for (int m = 0; m < a.length; m++) {
if (a[m].equals(b[m])) {
} else {
x++;
Log.d("Home", a[m] + " -- " + b[m]);
//to print difference
if (a[m].length() < b[m].length())
Log.d("Home", "" + StringUtils.difference(a[m], b[m]));
else
Log.d("Home", "" + StringUtils.difference(b[m], a[m]));
}
}
Output
08-26 17:51:26.949: DEBUG/Home(17900): 12 -- 123
08-26 17:51:26.949: DEBUG/Home(17900): Difference String : 3
08-26 17:51:26.949: DEBUG/Home(17900): No. of differences : 1
08-26 17:51:26.949: DEBUG/Home(17900): Files are not equal

Try using java.util.Scanner
while (sc1.hasNext() && sc2.hasNext()) {
String str1 = sc1.next();
String str2 = sc2.next();
if (!str1.equals(str2))
System.out.println(str1 + " != " + str2);
}

Change your while loop to the following:
while (scanFile.hasNextLine() && scanFileT.hasNextLine())
{
if(scanFileT.nextLine().equals(scanFile.nextLine()))
{
// The lines are equal.
} else {
// The lines are not equal.
}
}
if(scanFile.hasNextLine() || scanFileT.hasNextLine())
{
// If more lines remain in one of the files, they are not equal.
} else {
// If no content remains in both files, they are equal.
}
Depending on the size of your file, I would recommend some optimisation like checking the file sizes before you go through them line by line.
The overall logic reads as follows; if both have another line, compare it to see if it is equal. If they don't have another line, check if one of them has lines remaining, if so, they are not equal.
Update
After clarifying the objective of the comparison in chat, see the comments to this question, I have come to the conclusion that another comparison would be more effective and, as a matter of fact, correct. The comparison algorithm above works great if comparing the structure of text but not if comparing a data vector which may or may not be sorted. After some discussion, we came to the conclusion that data needs to be sorted or the comparison will blow the complexity to at least O(n^2)which could be done in O(2n) if the data is sorted. Here the algorithm's skeleton:
if(! scanGroupFriends.hasNextLine())
{
//simple sanity check to see if we need to compare at all. In this case, add all friends.
} else {
String nextFriend = scanGroupFriends.nextLine();
while(scanAllFriends.hasNextLine())
{
if(scanAllFriends.nextLine().equals(nextFriend))
{
// Friend already figures, do not add him and advance the list of group friends.
if(scanGroupFriends.hasNextLine())
{
nextFriend = scanGroupFriends.nextLine();
} else {
// There are no more friends in the group, add all remaining friends to list to show.
break; // Terminate the `while` loop.
}
}
}
}
However, I personally think it is bad to make to many assumptions. What I would suggest is that the friends be saved in a Set, a TreeSet for example. Then, serialize the object rather than manually writing it to file. Sets are neat because they hold several interesting objects. For example, you could easily use the following code to remove all friends in a group from the set of all friends:
allFriends.removeAll(groupFriends);
However, be aware that this removes it from the set completely so you should make a copy beforehand.