Develop Reference

Android Studio - Random Number within range and no duplicates

I was working on a quiz app in Android studio..
I have 2 tables which are the solutions and questions..
In my game, I wanna create a random number in the range of this table without duplicates..
with this random number I update my questions and answers..
I try this code now to create numbers (with duplicates):
Random rand = new Random();
n = rand.nextInt(QuestionLibrary.mChoices.length) + 1;
here is the photo of my game

If you don't have much numbers, you can make a collection with all of them, shuffle and then take one by one from it.
If you have a lot of numbers, then better aproach would be to make an empty collection and add every number that random function returns if it already does not exists. If number already exists, get another one, and so on.
Please read more here:
https://stackoverflow.com/a/4040014/7270175
EDIT: added code snippet that reproduces MAX number of different random numbers without duplicates.
private static int MAX = 1000;
private static boolean[] numbers;
public static void main(String[] args) {
Random generator = new Random();
numbers = new boolean[MAX + 1];
for (int i = 0; i < MAX; i++) {
System.out.println(getRandomWithoutDuplicates(generator));
}
}
private static int getRandomWithoutDuplicates(Random generator) {
int randomNum;
do {
randomNum = generator.nextInt(MAX);
} while (numbers[randomNum]);
numbers[randomNum] = true;
return randomNum;
}

payUmoney integration is giving an error

After logging in, it's generating a hash value, but still giving error "Some problem occurred! try again".
PayUmoneySdkInitilizer.PaymentParam.Builder builder =
new PayUmoneySdkInitilizer.PaymentParam.Builder();
builder.setAmount(10.0)
.setTnxId("0nf7" + System.currentTimeMillis())
.setPhone(<My phone>)
.setProductName("product_name")
.setFirstName(<My Name>)
.setEmail(<My email>)
.setsUrl("https://www.payumoney.com/mobileapp/payumoney/success.php")
.setfUrl("https://www.payumoney.com/mobileapp/payumoney/failure.php")
.setUdf1("").setUdf2("").setUdf3("").setUdf4("").setUdf5("")
.setIsDebug(false)
.setKey(<mykey>)
.setMerchantId(<my debug merchant id>);
String tnxId="0nf7" + System.currentTimeMillis();
PayUmoneySdkInitilizer.PaymentParam paymentParam = builder.build();
String hashSequence = "<...>|"+tnxId+"|10.0|product_name|<My name>|<My email>|||||||||||salt";
String serverCalculatedHash= hashCal("SHA-512", hashSequence);
Toast.makeText(getApplicationContext(),
serverCalculatedHash, Toast.LENGTH_SHORT).show();
paymentParam.setMerchantHash(serverCalculatedHash);
// calculateServerSideHashAndInitiatePayment(paymentParam);
PayUmoneySdkInitilizer.startPaymentActivityForResult(TrayActivity.this, paymentParam);
public static String hashCal(String type, String str) {
byte[] hashseq = str.getBytes();
StringBuffer hexString = new StringBuffer();
try {
MessageDigest algorithm = MessageDigest.getInstance(type);
algorithm.reset();
algorithm.update(hashseq);
byte messageDigest[] = algorithm.digest();
for (int i = 0; i<messageDigest.length; i++) {
String hex = Integer.toHexString(0xFF &messageDigest[i]);
if (hex.length() == 1) { hexString.append("0"); }
hexString.append(hex);
}
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} return hexString.toString();
}

You use in the code:
.setTnxId("0nf7" + System.currentTimeMillis())
And then later:
String tnxId="0nf7" + System.currentTimeMillis();
Probably not the only problem, but do you really want to use two different values for these (the time may change between the two calls)? Didn't you want the same tnxId in both cases?
TransactionIdProvider.java:
import java.util.Locale;
public class TransactionIdProvider {
private final static String DEFAULT_PREFIX = "ID";
// Convenient prime number for incrementing the counter
private final static long ID_ADD = 0xF0AD; // "f*ck off and die"
// 64b counter with non-trivial start value
private static long idCounter = 0x0101F00DDEADBEEFL;
/**
* Returns ID consisting of prefix string and 64b counter interleaved
* with 32b per-4s-timestamp.
*
* May produce identical ID (collision) when:
* 1) class is reloaded within 4s
* (to fix: serialize "idCounter" upon shutdown/restart of VM, or
* modify prefix per start of VM)
* 2) more than 2^64 IDs are requested within 4s (no fix, unexpected)
* 3) more than 2^64 IDs are requested after cca. 550 years.
* (no fix, unexpected)
* 4) more than one static instance of TransactionIdProvider is used
* (two or more VMs running the app) (to fix put different prefix in
* every VM/server running this)
*
* Length of returned ID is prefix.length() + 24 alphanumeric symbols.
*/
public static synchronized String getNewId(final String prefix) {
idCounter += ID_ADD; // increment counter
// get 32b timestamp per ~4s (millis/4096) (good for ~550 years)
final int timeStamp = (int)(System.currentTimeMillis()>>12);
final int idPart1 = (int)(idCounter>>32);
final int idPart2 = (int)(idCounter);
return String.format(Locale.US, "%s%08X%08X%08X",
prefix, idPart1, timeStamp, idPart2);
}
public static String getNewId() {
return getNewId(DEFAULT_PREFIX);
}
}
Not sure how much usable is this one, and if the ID may be so long. Feel free to use/modify it any way you wish.
Also I wonder, whether I didn't forget about something important, but can't recall anything.
The security aspect of this one is still quite weak, as within 4s time span the ID will be like simple addition, but at least it's not producing 1, 2, 3... series.
Did found some SDK docs, looks like txnId may be 25 chars long, so you have 1 char for prefix only. Or cut down on timestamp, using %07X in format and masking value with 0x0FFFFFFF, that would make it repeat every ~34 years -> 2 letters for prefix. Or change counter to 32b int, should be still more than enough, unless you expect thousands of transactions per second -> that would remove 8 chars. Or base32/base64 the whole ID to shorten it (depends what alphabet is legal for content)...
Or whatever... already spent enough time with this. Hire a pro.

How to get byte by byte from byte array

I am getting response from server in string format like
V1YYZZ0x0000010x0D0x00112050x0C152031962061900x0D410240x0E152031962061900x0F410240x1021TATADOCOMOINTERNET101
Then I am converting it in to byte array because i need to get value from this byte by byte.
I tried to use
Arrays.copyOfRange(original,
from , to);
but it work on index basis not on byte basis.
I also tried following solution but it also truncating String(if I use string instead of byte[]) on length basis.
public static String truncateWhenUTF8(String s, int maxBytes) {
int b = 0;
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
// ranges from http://en.wikipedia.org/wiki/UTF-8
int skip = 0;
int more;
if (c <= 0x007f) {
more = 1;
} else if (c <= 0x07FF) {
more = 2;
} else if (c <= 0xd7ff) {
more = 3;
} else if (c <= 0xDFFF) {
// surrogate area, consume next char as well
more = 4;
skip = 1;
} else {
more = 3;
}
if (b + more > maxBytes) {
return s.substring(0, i);
}
b += more;
i += skip;
}
return s;
}
I know how to calculate string in byte length but it giving only full string length in byte like
Here is how I need to extract packet on byte basis.
Above codes and parameters is only example. I need to get byte by byte from string/byte array.
I searched lot but didn't get any solution or link which I can refer. I am not getting how to split string using byte length because I know byte length for each parameter and for value also.
Please give me any reference or hint.

To determine what is equal to one byte in a String is not trivial. Your String contains bytes in hexadecimal text form: 0x0D (one byte, equal to 13), but also contains values as substrings. For example 1024 can be interpreted as an integer which in this case fits into 2 bytes, but could also be interpreted as a text made up by 4 chars, totaling to 8 bytes.
Anyways, I would split the string using a regular expression, and then further split the parts to length and value:
String message = "V1YYZZ0x0000010x0D0x00112050x0C152031962061900x0D41024"+
"0x0E152031962061900x0F410240x1021TATADOCOMOINTERNET101";
String regex = "(0)(x)(\\w\\w)";
String[] parts = message.split(regex);
Log.d(TAG,"HEADER = "+parts[0]);
for (int i=1; i<parts.length; i++) {
String s = parts[i];
// Only process if it has length > 0
if (s.length()>0) {
String len = "", val = "";
// String s is now in format LVVVV where L is the length, V is the value
if (s.length() < 11) {
// 1 character indicates length, up to 9 contains value
len = s.substring(0, 1);
val = s.substring(1);
} else if (s.length() > 10) {
// 2 characters indicate length, up to 99 contains value
len = s.substring(0, 2);
val = s.substring(2);
} else if (s.length() > 101) {
// 3 characters indicate length, up to 999 contains value
len = s.substring(0, 3);
val = s.substring(3);
}
Log.d(TAG, "Length: " + len + " Value: " + val);
}
}
This produces the following output:
D/Activity: HEADER = V1YYZZ
D/Activity: Length: 0 Value: 001
D/Activity: Length: 1 Value: 1205
D/Activity: Length: 15 Value: 203196206190
D/Activity: Length: 4 Value: 1024
D/Activity: Length: 15 Value: 203196206190
D/Activity: Length: 4 Value: 1024
D/Activity: Length: 21 Value: TATADOCOMOINTERNET101
Then you can check the packages (the first two package in the header is not needed), convert Strings to whatever you would like (e.g. Integer.parseInt(val))
If you explain the structure of the header (V1YYZZ0x0000010x0D0x0011205), I can improve my answer to find the message count.

I think it is doable with Scanner
import java.util.Scanner;
public class Library {
public static void main(String[] args) {
String s = "V1YYZZ0x0000010x0D0x001120"
+ "50x0C152031962061900x0D410240x0E152031962061900x0F410240x1"
+ "021TATADOCOMOINTERNET101";
// Skip first 9? bytes. I'm not sure how you define them
// so I just assumed it is 26 chars long.
s = s.substring(26, s.length());
System.out.println(s);
Scanner scanner = new Scanner(s);
// Use byte as delimiter i.e. 0xDC, 0x00
// Maybe you should use smth like 0x[\\da-fA-F]{2}
// And if you want to know that byte, you should use
// just 0x and get first 2 chars later
scanner.useDelimiter("0x\\w{2}");
// Easily extracted
int numberOfParams = scanner.nextInt();
for (int i = 0; i < numberOfParams; i++) {
String extracted = scanner.next();
// Length of message
int l = extracted.length();
boolean c = getLength(l) == getLength(l - getLength(l));
l -= getLength(l);
l = c ? l : l-1;
System.out.println("length="
+ extracted.substring(0, extracted.length()-l));
System.out.println("message="
+ extracted.substring(extracted.length()-l, extracted.length()));
}
// close the scanner
scanner.close();
}
// Counting digits assuming number is decimal
private static int getLength(int l) {
int length = (int) (Math.log10(l) + 1);
System.out.println("counted length = " + length);
return length;
}
}
We definitely need more information about rules, how string is formed. And what exactly you need to do. This code might be good enough you. And without comments it is really short and simple.

This is not a answer to accessing a byte array byte by byte, but is an answer for the situation in which you find yourself.
Your explanation and description have the appearance of being confused as to what it is that you are really getting from the server (e.g. it is quite hard to represent "V1YYZZ0x0000010x0D0x001120" as a 9 byte field (note it probably ends on the 2, not the 0)). Alternately, that you are using the wrong method to get it from the server, or not getting it as the intended data type.
Your code indicates that you believe that what you are getting is a UTF8 string. The data shown in your question does not appear to indicate that it is intended to be in that format.
Keep in mind when doing something like this that some other programmer had to create structure for the data that you are seeing. They had to define it somewhere with the intent that it be able to be decoded by their intended recipients. Unless there are other considerations (security, minimal bandwidth, etc.), such formats are usually defined in a way that is both easy to encode and decode.
The existence of the multiple "0x"-ASCII-encoded hexadecimal numbers --particularly the single byte representing the parameter (called "varam" in your graphic)-- strongly implies that this data was intended to be interpreted as a ASCII encoded string. While that might not be the case, it should be kept in mind when looking at the problem from a larger perspective.
You are having to put too much effort into decoding the information you are getting from the server. It, probably, should be relatively easy unless there are considerations why it would have intentionally been made difficult.
All of this indicates that the real problem exists in an area for which you have provided us with no information.
Step back:
Think about things like:
How are you receiving this from the server (what function/interface)?
In the call requesting the information from the server is there a way to specify the encoding type be bytes, an ASCII string, or some other format that is easier to deal with than UTF8? At a minimum, it appears to be clear that the data was not intended to be handled as a UTF8 string. There should be a way for you to get it without it having been converted to UTF8.
Also, you should try to find an actual specification for the format of the data. You have not explained much about the source, so it may be you are reverse-engineering something and have no access to specifications.
Basically, it looks like this is a problem where it might be a good idea to step back and ask if you are starting from the point that makes it easiest to solve and if you are headed in the right direction for doing so.

I'm sure I'm missing something obvious...
String.getBytes();
And if you want to process it in order taking defined objects from the array, just wrap using
ByteBuffer.wrap();
The result being something along the lines of:
String s = "OUTPUT FROM SERVER";
byte[] bytes = s.getBytes();
ByteBuffer bb = ByteBuffer.wrap(bytes);
What did I miss from the initial question? :/

Separating the words after the last integer in a large String

I've seen many people do similar to this in order to get the last word of a String:
String test = "This is a sentence";
String lastWord = test.substring(test.lastIndexOf(" ")+1);
I would like to do similar but get the last few words after the last int, it can't be hard coded as the number could be anything and the amount of words after the last int could also be unlimited. I'm wondering whether there is a simple way to do this as I want to avoid using Patterns and Matchers again due to using them earlier on in this method to receive a similar effect.
Thanks in advance.

I would like to get the last few words after the last int.... as the number could be anything and the amount of words after the last int could also be unlimited.
Here's a possible suggestion. Using Array#split
String str = "This is 1 and 2 and 3 some more words .... foo bar baz";
String[] parts = str.split("\\d+(?!.*\\d)\\s+");
And now parts[1] holds all words after the last number in the string.
some more words .... foo bar baz

What about this one:
String test = "a string with a large number 1312398741 and some words";
String[] parts = test.split();
for (int i = 1; i < parts.length; i++)
{
try
{
Integer.parseInt(parts[i])
}
catch (Exception e)
{
// this part is not a number, so lets go on...
continue;
}
// when parsing succeeds, the number was reached and continue has
// not been called. Everything behind 'i' is what you are looking for
// DO YOUR STUFF with parts[i+1] to parts[parts.length] here
}

BigInteger q = new BigInteger(8, 10, new Random()); is not producing expected result in Android

BigInteger q = new BigInteger(8, 10, new Random()); is giving me random numbers as expected every time while running from my Desktop but not in Android.
in Android I am always getting only same output instead of random number. Please help me to get random BigIntegr.
for your info:
int randQ = (int) (Math.random() * 9);
for (int r = 0; r < randQ; r++) {
q = q.nextProbablePrime();
}
is the quick fix that I did and I am not happy with this fix since it is consuming extra time.
your suggestions are highly appreciated

This is a very common problem, independent of language or platform.
You must reuse the instance of Random() to get random numbers each time. The default constructor will seed the pseudo-random number generator with the current time. The current time doesn't change very quickly with respect to your program, so you keep getting the same number until the clock ticks up.
If you don't re-seed, it will give you different numbers each time you ask for another value. You can avoid re-seeding by reusing the instance, and calling:
Random random = new Random(); // reuse this instance...
int value = random.nextInt(); // use these values instead of new Random()
See: http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Random.html

EDITED
Instead use:
// creates random object with current instant as seed
Random generator = new Random((new Date()).getTime());
BigInteger q = new BigInteger(8, 10, generator);