Develop Reference

Convert String representation to minimal Number Object

Having a String representation of a number(no decimals), what's the best way to convert it to either one of java.lang.Integer or java.lang.Long or java.math.BigInteger? The only condition is that the converted type should be of minimal datatype required to hold the number.
I've this current implementation that works fine, but I would like to know if there's a better code without exception handling.
package com.stackoverflow.programmer;
import java.math.BigInteger;
public class Test {
public static void main(String[] args) {
String number = "-12121111111111111";
Number numberObject = null;
try {
numberObject = Integer.valueOf(number);
} catch (NumberFormatException nfe) {
System.out.println("Number will not fit into Integer type. Trying Long...");
try {
numberObject = Long.valueOf(number);
} catch (NumberFormatException nfeb) {
System.out.println("Number will not fit into Long type. Trying BigInteger...");
numberObject = new BigInteger(number);
}
}
System.out.println(numberObject.getClass() + " : "
+ numberObject.toString());
}
}

From what you said, here is what I would have done:
import java.math.BigInteger;
import java.util.Arrays;
import java.util.List;
public class TestSO09_39463168_StringToMinimalNumber {
public static void main(String[] args) {
List<String> strNumbers = Arrays.asList("0", //int
"123", //int
"-456", //int
"2147483700", // Long
"-2147483700", // Long
"9223372036854775900", //BigInt
"-9223372036854775900" //BigInt
);
for(String strNumber : strNumbers){
Number number = stringToMinimalNumber(strNumber);
System.out.println("The string '"+strNumber+"' is a "+number.getClass());
}
}
public static Number stringToMinimalNumber(String s){
BigInteger tempNumber = new BigInteger(s);
if(tempNumber.compareTo(BigInteger.valueOf(Long.MAX_VALUE)) > 0 || tempNumber.compareTo(BigInteger.valueOf(Long.MIN_VALUE)) < 0){
return tempNumber;
} else if(tempNumber.compareTo(BigInteger.valueOf(Integer.MAX_VALUE)) > 0 || tempNumber.compareTo(BigInteger.valueOf(Integer.MIN_VALUE)) < 0){
return tempNumber.longValue(); //Autobox to Long
} else {
return tempNumber.intValue(); //Autobox to Integer
}
}
}
You must use a temporary BigInteger, or else you'll end up with lazarov's solution, which is correct, but you can't really do something like that for reason mentionned in the comments.
Anyway, every BigInteger (the ones that are not returned) will be garbage collected. As for autoboxing, I don't think it's that of a bad thing. You could also make "BigInteger.valueOf(Long.MAX_VALUE))" as a constant. Maybe the compiler or the JVM will do this on its own.
I'm not really sure of how efficient it is, and using only BigInteger might be a good idea (as Spotted did), because I serioulsy doubt it would really improve the rest of your code to use the right size, and it might even be error prone if you try to use these Numbers with each other ... But again, it all depend on what you need. (and yes, using Exception as flow control is a really bad idea, but you can add a try catch on the BigInteger tempNumber = new BigInteger(s); to throw your own exception if s is not a number at all)
For recreational purpose, I have made the solution without using a BigInteger, and only with String parsing (this is still not what I recommand to do, but it was fun :)
public static final String INT_MAX_VALUE = "2147483647";
public static final String LONG_MAX_VALUE = "9223372036854775807";
public static Number stringToMinimalNumberWithoutBigInteger(String numberStr){
//Removing the minus sign to test the value
String s = (numberStr.startsWith("-") ? numberStr.substring(1,numberStr.length()) : numberStr);
if(compareStringNumber(s, LONG_MAX_VALUE) > 0){
return new BigInteger(numberStr);
} else if(compareStringNumber(s, INT_MAX_VALUE) > 0){
return new Long(numberStr);
} else {
return new Integer(numberStr);
}
}
//return postive if a > b, negative if a < b, 0 if equals;
private static int compareStringNumber(String a, String b){
if(a.length() != b.length()){
return a.length() - b.length();
}
for(int i = 0; i < a.length(); i++){
if( a.codePointAt(i) != b.codePointAt(i) ){ //Or charAt()
return a.codePointAt(i) - b.codePointAt(i);
}
}
return 0;
}

Please don't use exceptions for handling flow control, this is a serious anti-pattern (also here).
As you mentionned in the comments, the real thing you've been asked is to convert a List<String> into a List<Number>.
Also, if I understand correctly, you know that:
You should encounter only numbers without decimals
The biggest value you can encounter is possibly unbound
Based on that, the following method will do the job in a more clever way:
private static List<Number> toNumbers(List<String> strings) {
return strings.stream()
.map(BigInteger::new)
.collect(Collectors.toList());
}
Eidt: if you're not very familiar with the stream concept, here's the equivalent code without streams:
private static List<Number> toNumbers(List<String> strings) {
List<Number> numbers = new ArrayList<>();
for (String s : strings) {
numbers.add(new BigInteger(s));
}
return numbers;
}

Well if you want to do it "by hand" try something like this:
We define the max values as strings :
String intMax = "2147483647";
String longMax = "9223372036854775807";
and our number:
String ourNumber = "1234567890"
Now our logic will be simple :
We will check lenghts of strings firstly
If our numbers length < int max length : IT IS INT
If our numbers length == int max length : Check is it INT or LONG
If our numbers length > int max length :
3.1 If our numbers length < long max length : IT IS LONG
3.2 If our numbers length == long max length : Check is it LONG or BIG INTEGER
3.3 If our numbers length > long max length : IT IS BIG INTEGER
The code should look something like this (I have not tried to compile it may have syntax or other errors) :
if(ourNumber.lenght() < intMax.length ){
System.out.println("It is an Integer");
} else if(ourNumber.lenght() == intMax.length){
// it can be int if the number is between 2000000000 and 2147483647
char[] ourNumberToCharArray = ourNumber.toCharArray();
char[] intMaxToCharArray = intMax.toCharArray();
int diff = 0;
for(int i = 0; i < ourNumberToCharArray.length; i++) {
diff = Character.getNumericValue(intMaxToCharArray[i]) - Character.getNumericValue(ourNumberToCharArray[i]);
if(diff > 0) {
System.out.println("It is a Long");
break;
} else if(diff < 0) {
System.out.println("It is an Integer");
break;
}
}
if(diff == 0){
System.out.println("It is an Integer");
}
} else {
if(ourNumber.lenght() < longMax.length()) {
System.out.println("It is a Long");
} else if(ourNumber.lenght() == longMax.length()){
char[] ourNumberToCharArray = ourNumber.toCharArray();
char[] longMaxToCharArray = longMax.toCharArray();
int diff = 0;
for(int i = 0; i < ourNumberToCharArray.length; i++) {
diff = Character.getNumericValue(longMaxToCharArray[i]) - Character.getNumericValue(ourNumberToCharArray[i]);
if(diff > 0) {
System.out.println("It is a BigInteger");
break;
} else if(diff < 0) {
System.out.println("It is a Long");
break;
}
}
if(diff == 0){
System.out.println("It is a Long");
}
} else {
System.out.println("It is a BigInteger");
}
}
Then logic that checks if the numbers match or not is the same in both cases you can but it in a function for example.

String index out of range in Java

I am aware there are multiple threads like my assignment below, but I just can't figure it out. I can't exactly figure out the mistake. Help would be appreciated.
I am trying to do this program:
Everything works fine unless I input the same chains or similar (for example ACTG and ACTG or ACTG and ACTGCCCC), when it tells me
string index out of range
This is that part of my code:
int tries=0;
int pos=-1;
int k;
for (int i=0; i<longDNA.length(); i++) {
tries=0;
k=i;
for (int j=0; j<shortDNA.length(); j++) {
char s=shortDNA.charAt(j);
char l=longDNA.charAt(k);
if (canConnect(s,l)) {
tries+=1;
k+=1;
}
}
if (tries==shortDNA.length()-1) {
pos=i-1;
break;
}
}

Let's call the two DNA strings longer and shorter. In order for shorter to attach somewhere on longer, a sequence of bases complementary to shorter must be found somewhere in longer, e.g. if there is ACGT in shorter, then you need to find TGCA somewhere in longer.
So, if you take shorter and flip all of its bases to their complements:
char[] cs = shorter.toCharArray();
for (int i = 0; i < cs.length; ++i) {
// getComplement changes A->T, C->G, G->C, T->A,
// and throws an exception in all other cases
cs[i] = getComplement(cs[i]);
}
String shorterComplement = new String(cs);
For the examples given in your question, the complement of TTGCC is AACGG, and the complement of TGC is ACG.
Then all you have to do is to find shorterComplement within longer. You can do this trivially using indexOf:
return longer.indexOf(shorterComplement);
Of course, if the point of the exercise is to learn how to do string matching, you can look at well-known algorithms for doing the equivalent of indexOf. For instance, Wikipedia has a category for String matching algorithms.

I tried to replicate your full code as fast as I could, I'm not sure if I fixed the problem but you don't get any errors.
Please try it and see if it works.
I hope you get this in time and good luck!
import java.util.Arrays;
public class DNA {
public static void main(String[] args) {
System.out.println(findFirstMatchingPosition("ACTG", "ACTG"));
}
public static int findFirstMatchingPosition(String shortDNA, String longDNA) {
int positionInLong = 0;
int positionInShort;
while (positionInLong < longDNA.length()) {
positionInShort = 0;
while(positionInShort < shortDNA.length()) {
String s = shortDNA.substring(positionInShort, positionInShort + 1);
if(positionInShort + positionInLong + 1 > longDNA.length()) {
break;
}
String l = longDNA.substring(positionInShort + positionInLong, positionInShort + positionInLong + 1);
if(canConnect(s, l)) {
positionInShort++;
if(positionInShort == shortDNA.length()) {
return positionInLong;
}
} else {
break;
}
}
positionInLong++;
if(positionInLong == longDNA.length()) {
return -1;
}
}
return -1;
}
private static String[] connections = {
"AT",
"TA",
"GC",
"CG"
};
private static boolean canConnect(String s, String l) {
if(Arrays.asList(connections).contains((s+l).toUpperCase())) {
return true;
} else {
return false;
}
}
}

I finally changed something with the k as Faraz had mentioned above to make sure the charAt does not get used when k overrides the length of the string and the program worked marvelously!
The code was changed to the following:
int tries=0;
int pos=-1;
int k;
for (int i=0; i<longDNA.length(); i++) {
tries=0;
k=i;
for (int j=0; j<shortDNA.length(); j++) {
if (k<longDNA.length()) {
char s=shortDNA.charAt(j);
char l=longDNA.charAt(k);
if ((s=='A' && l=='T') || (s=='T' && l=='A') || (s=='G' && l=='C') || (s=='C' && l=='G')) {
tries+=1;
k+=1;
}
}
}
if (tries==shortDNA.length()) {
pos=i;
break;
}
}
I am not sure how aesthetically pleasing or correct this excerpt is but - it completely solved my problem, and just 2 minutes before the deadline! :)
A huge thanks to all of you for spending some time to help me!!

Correcting and Condensing Java Program

I think I've almost figured out my java program. It is designed to read a text file and find the largest integer by using 10 different threads. I'm getting this error though:
Error:(1, 8) java: class Worker is public, should be declared in a file named Worker.java
I feel my code may be more complex than it needs to be so I'm trying to figure out how to shrink it down in size while also fixing the error above. Any assistance in this matter would be greatly appreciated and please let me know if I can clarify anything. Also, does the "worker" class have to be a seperate file? I added it to the same file but getting the error above.
import java.io.BufferedReader;
import java.io.FileReader;
public class datafile {
public static void main(String[] args) {
int[] array = new int[100000];
int count;
int index = 0;
String datafile = "dataset529.txt"; //string which contains datafile
String line; //current line of text file
try (BufferedReader br = new BufferedReader(new FileReader(datafile))) { //reads in the datafile
while ((line = br.readLine()) != null) { //reads through each line
array[index++] = Integer.parseInt(line); //pulls out the number of each line and puts it in numbers[]
}
}
Thread[] threads = new Thread[10];
worker[] workers = new worker[10];
int range = array.length / 10;
for (count = 0; count < 10; count++) {
int startAt = count * range;
int endAt = startAt + range;
workers[count] = new worker(startAt, endAt, array);
}
for (count = 0; count < 10; count++) {
threads[count] = new Thread(workers[count]);
threads[count].start();
}
boolean isProcessing = false;
do {
isProcessing = false;
for (Thread t : threads) {
if (t.isAlive()) {
isProcessing = true;
break;
}
}
} while (isProcessing);
for (worker worker : workers) {
System.out.println("Max = " + worker.getMax());
}
}
}
public class worker implements Runnable {
private int startAt;
private int endAt;
private int randomNumbers[];
int max = Integer.MIN_VALUE;
public worker(int startAt, int endAt, int[] randomNumbers) {
this.startAt = startAt;
this.endAt = endAt;
this.randomNumbers = randomNumbers;
}
#Override
public void run() {
for (int index = startAt; index < endAt; index++) {
if (randomNumbers != null && randomNumbers[index] > max)
max = randomNumbers[index];
}
}
public int getMax() {
return max;
}
}

I've written a few comments but I'm going to gather them all in an answer so anyone in future can see the aggregate info:
At the end of your source for the readtextfile class (which should be ReadTextile per java naming conventions) you have too many closing braces,
} while (isProcessing);
for (Worker worker : workers) {
System.out.println("Max = " + worker.getMax());
}
}
}
}
}
The above should end on the first brace that hits the leftmost column. This is a good rule of thumb when making any Java class, if you have more than one far-left brace or your last brace isn't far-left you've probably made a mistake somewhere and should go through checking your braces.
As for your file issues You should have all your classes named following Java conventions and each class should be stored in a file called ClassName.java (case sensitive). EG:
public class ReadTextFileshould be stored in ReadTextFile.java
You can also have Worker be an inner class. To do this you could pretty much just copy the source code into the ReadTextFile class (make sure it's outside of the main method). See this tutorial on inner classes for a quick overview.
As for the rest of your question Code Review SE is the proper place to ask that, and the smart folks over there probably will provide better answers than I could. However I'd also suggest using 10 threads is probably not the most efficient way in to find the largest int in a text file (both in development and execution times).

Java array sorting in reverse! Need to reverse the reverse

Right now I have my array sorting (which is better than getting an error) except it is sorting in the reverse than what I want it to sort in.
public static void sortDatabase(int numRecords, String[] sDeptArr,
int[] iCourseNumArr, int[] iEnrollmentArr)
{
System.out.println("\nSort the database. \n");
String sTemp = null;
int iTemp = 0;
int eTemp = 0;
String a, b = null;
for(int i=0; i<numRecords; i++)
{
int iPosMin = i+1;
for(int j=iPosMin; j<numRecords; j++)
{
a = sDeptArr[i];
b = sDeptArr[iPosMin];
if(a.compareTo(b) > 0)
{
sTemp= sDeptArr[j];
sDeptArr[j] = sDeptArr[iPosMin];
sDeptArr[iPosMin] = sTemp;
iTemp = iCourseNumArr[j];
iCourseNumArr[j] = iCourseNumArr[iPosMin];
iCourseNumArr[iPosMin] = iTemp;
eTemp = iEnrollmentArr[j];
iEnrollmentArr[j] = iEnrollmentArr[iPosMin];
iEnrollmentArr[iPosMin] = eTemp;
}
else if(sDeptArr[j].equals(sDeptArr[iPosMin]) && !(iCourseNumArr[j] < iCourseNumArr[iPosMin]))
{
sTemp= sDeptArr[i];
sDeptArr[i] = sDeptArr[iPosMin];
sDeptArr[iPosMin] = sTemp;
iTemp = iCourseNumArr[i];
iCourseNumArr[i] = iCourseNumArr[iPosMin];
iCourseNumArr[iPosMin] = iTemp;
eTemp = iEnrollmentArr[i];
iEnrollmentArr[i] = iEnrollmentArr[iPosMin];
iEnrollmentArr[iPosMin] = eTemp;
}
else continue;
}
}
}
Again, no array lists or array.sorts. I need just to reverse how this is sorting but I have no idea how.

just do a.compareTo(b) < 0 instead of the > 0
EDIT: I've figured out the problem. But since this is homework (thanks for being honest), I won't post my solution, but here are a few tips:
You are doing selection sort. The algorithm isn't as complicated as you made it. You only have to swap if the two elements you are checking are in the wrong order. I see you have 3 branches there, no need.
Take a look at when you are assigning a and b. Through the inner loop, where j is changing, a and b never change, because i and iPosMin stay the same. I hope that helps.
It's always good to break your algorithm down to discreet parts that you know works by extracting methods. You repeat the same swap code twice, but with different arguments for indices. Take that out and just make a:
-
// swaps the object at position i with position j in all arrays
private static void swap(String[] sDeptArr, int[] iCourseNumArr, int[] iEnrollmentArr, int i, int j)
Then you'll see you're code get a lot cleaner.

First I'd say you need to build a data structure to encapsulate the information in your program. So let's call it Course.
public class Course {
public String department;
public Integer courseNumber;
public Integer enrollment;
}
Why not use the built in sort capabilities of Java?
List<Course> someArray = new ArrayList<Course>();
...
Collections.sort( someArray, new Comparator<Course>() {
public int compare( Course c1, Course c2 ) {
int r = c1.compareTo( c2 );
if( r == 0 ) { /* the strings are the same sort by something else */
/* using Integer instead of int allows us
* to compare the two numbers as objects since Integer implement Comparable
*/
r = c1.courseNumber.compareTo( c2.courseNumber );
}
return r;
}
});
Hope that gets you an A on your homework. Oh and ditch the static Jr. Maybe one day your prof can go over why statics are poor form.

Hmm... I wonder what would happen of you altered the line that reads if(a.compareTo(b) > 0)?

How to generate a random String in Java [duplicate]

This question already has answers here:
How to generate a random alpha-numeric string
(46 answers)
Closed 6 years ago.
I have an object called Student, and it has studentName, studentId, studentAddress, etc. For the studentId, I have to generate random string consist of seven numeric charaters,
eg.
studentId = getRandomId();
studentId = "1234567" <-- from the random generator.
And I have to make sure that there is no duplicate id.

Generating a random string of characters is easy - just use java.util.Random and a string containing all the characters you want to be available, e.g.
public static String generateString(Random rng, String characters, int length)
{
char[] text = new char[length];
for (int i = 0; i < length; i++)
{
text[i] = characters.charAt(rng.nextInt(characters.length()));
}
return new String(text);
}
Now, for uniqueness you'll need to store the generated strings somewhere. How you do that will really depend on the rest of your application.

This is very nice:
http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/RandomStringUtils.html - something like RandomStringUtils.randomNumeric(7).
There are 10^7 equiprobable (if java.util.Random is not broken) distinct values so uniqueness may be a concern.

You can also use UUID class from java.util package, which returns random uuid of 32bit characters String.
java.util.UUID.randomUUID().toString()
http://java.sun.com/j2se/1.5.0/docs/api/java/util/UUID.html

Random ran = new Random();
int top = 3;
char data = ' ';
String dat = "";
for (int i=0; i<=top; i++) {
data = (char)(ran.nextInt(25)+97);
dat = data + dat;
}
System.out.println(dat);

I think the following class code will help you. It supports multithreading but you can do some improvement like remove sync block and and sync to getRandomId() method.
public class RandomNumberGenerator {
private static final Set<String> generatedNumbers = new HashSet<String>();
public RandomNumberGenerator() {
}
public static void main(String[] args) {
final int maxLength = 7;
final int maxTry = 10;
for (int i = 0; i < 10; i++) {
System.out.println(i + ". studentId=" + RandomNumberGenerator.getRandomId(maxLength, maxTry));
}
}
public static String getRandomId(final int maxLength, final int maxTry) {
final Random random = new Random(System.nanoTime());
final int max = (int) Math.pow(10, maxLength);
final int maxMin = (int) Math.pow(10, maxLength-1);
int i = 0;
boolean unique = false;
int randomId = -1;
while (i < maxTry) {
randomId = random.nextInt(max - maxMin - 1) + maxMin;
synchronized (generatedNumbers) {
if (generatedNumbers.contains(randomId) == false) {
unique = true;
break;
}
}
i++;
}
if (unique == false) {
throw new RuntimeException("Cannot generate unique id!");
}
synchronized (generatedNumbers) {
generatedNumbers.add(String.valueOf(randomId));
}
return String.valueOf(randomId);
}
}

The first question you need to ask is whether you really need the ID to be random. Sometime, sequential IDs are good enough.
Now, if you do need it to be random, we first note a generated sequence of numbers that contain no duplicates can not be called random. :p Now that we get that out of the way, the fastest way to do this is to have a Hashtable or HashMap containing all the IDs already generated. Whenever a new ID is generated, check it against the hashtable, re-generate if the ID already occurs. This will generally work well if the number of students is much less than the range of the IDs. If not, you're in deeper trouble as the probability of needing to regenerate an ID increases, P(generate new ID) = number_of_id_already_generated / number_of_all_possible_ids. In this case, check back the first paragraph (do you need the ID to be random?).
Hope this helps.

Many possibilities...
You know how to generate randomly an integer right?
You can thus generate a char from it... (ex 65 -> A)
It depends what you need, the level of randomness, the security involved... but for a school project i guess getting UUID substring would fit :)