Develop Reference

Finding the intersection between two date ranges in Java (programatically)

I would like to calculate the number of the overlapping days between two date ranges. The 2 pairs of date ranges are read from the console in the format: yyyy-mm-dd;
For example, if the two dates are
2020-01-05
2020-03-31
and
2020-01-05
2020-03-20
the program should find the days between 2020-01-05 and 2020-03-20. However, it doesn't work. I would like to ask how can I fix this?
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
import java.util.Scanner;
public class Dates {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
String a = sc.nextLine();
String b = sc.nextLine();
String c = sc.nextLine();
String d = sc.nextLine();
LocalDate ldt1 = LocalDate.parse(a);
LocalDate ldt2 = LocalDate.parse(b);
LocalDate ldt3 = LocalDate.parse(c);
LocalDate ldt4 = LocalDate.parse(d);
System.out.println(ChronoUnit.DAYS.between(ldt1,ldt2,ldt3,ldt4));
}
}

It’s a little more complicated than that (not badly).
String i1StartStr = "2020-01-05";
String i1EndStr = "2020-03-31";
String i2StartStr = "2020-01-05";
String i2EndStr = "2020-03-20";
LocalDate i1Start = LocalDate.parse(i1StartStr);
LocalDate i1End = LocalDate.parse(i1EndStr);
LocalDate i2Start = LocalDate.parse(i2StartStr);
LocalDate i2End = LocalDate.parse(i2EndStr);
if (i1End.isBefore(i1Start) || i2End.isBefore(i2Start)) {
System.out.println("Not proper intervals");
} else {
long numberOfOverlappingDates;
if (i1End.isBefore(i2Start) || i2End.isBefore(i1Start)) {
// no overlap
numberOfOverlappingDates = 0;
} else {
LocalDate laterStart = Collections.max(Arrays.asList(i1Start, i2Start));
LocalDate earlierEnd = Collections.min(Arrays.asList(i1End, i2End));
numberOfOverlappingDates = ChronoUnit.DAYS.between(laterStart, earlierEnd);
}
System.out.println("" + numberOfOverlappingDates + " days of overlap");
}
Output from the code as it stands here is:
75 days of overlap
I have also used better variable names and have introduced validation of the intervals that the user inputs.
I know I was supposed to add some explanation here, but frankly, I find the code using java.time so clear to read in itself, I don’t know what needs to be explained. If you want the number of days inclusive of both start and end dates, remember to add 1 to the return value from ChronoUnit.DAYS.between(). Please follow up in the comments and let me know what further explanation will be appropriate.

Java.Lang.Double[] to Double[] issue for Polynomial from CSV

First of all thanks for your help in advance.
I'm writing an investment algorithm and am currently pre-processing CSV historical data. The end goal for this part of the process is to create a symmetrical co-variance matrix of 2k x 2k / 2 (2 million) entries.
The Java class I'm writing takes a folder of CSVs each with 8 bits of information, key ones being Date, Time & Opening stock price. Date & time have been combined into one 'seconds from delta' time measure and opening stock prices remain unchanged. The output CSV contains the above two pieces of information also with a filename index for later referencing.
In order to create the co-variance matrix each stock on the NYSE must have a price value for every time, if values are missing the matrix cannot be properly completed. Due to discrepancies between time entries in the historical training CSV, I have to use a polynomial function to estimate missed values, which then can be fed into the next process in the chain.
My problem sounds fairly simple and should be easy to overcome (I'm probably being a massive idiot). The polynomial package I'm using takes in two arrays of doubles (Double[] x, Double[] y). X pertaining to an array of the 'seconds past delta' time values of a particular stock and Y the corresponding price. When I try to feed these in I'm getting a type error as what I'm actually trying to input are 'java.lang.Double' objects. Can anyone help me with converting an array of the latter to an array of the former?
I realise there is a load of ridiculousness after the main print statement, these are just me tinkering trying to miraculously change the type.
Again thanks for your time, I look forward to your replies!
Please find the relevant method below:
public void main(String filePath) throws IOException {
String index = filePath;
index = index.replace("/Users/louislimon/Desktop/Invest Algorithm/Data/Samples US Stock Data/data-1/5 min/us/nyse stocks/1/", "");
index = index.replace(".us.txt", "");
File fout = new File("/Users/louislimon/Desktop/Invest Algorithm/Data.csv");
FileOutputStream fos = new FileOutputStream(fout);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(fos));
Reader in = new FileReader(filePath);
Iterable<CSVRecord> records;
try {
records = CSVFormat.EXCEL.withSkipHeaderRecord(true).parse(in);
} catch ( IOException ex ) {
System.out.println ( "[ERROR] " + ex );
return;
}
ZoneId zoneId = ZoneId.of("America/New_York");
boolean tmp = true;
Instant firstInstant = null; // Track the baseline against which we calculate the increasing time
ArrayList<Double> timeVals = new ArrayList<Double>();
ArrayList<Double> priceVals = new ArrayList<Double>();
for ( CSVRecord record : records ) {
if(tmp){
tmp = false;
}
else {
//System.out.println(record.toString());
String dateInput = record.get(0);
String timeInput = record.get(1);
Double price = Double.parseDouble(record.get(2));
LocalDate date = LocalDate.parse(dateInput);
LocalTime time = LocalTime.parse(timeInput);
//Double price = Double.parseDouble(priceInput);
LocalDateTime ldt = LocalDateTime.of(date, time);
ZonedDateTime zdt = ldt.atZone(zoneId);
Instant instant = zdt.toInstant(); // Use Instant (moment on the timeline in UTC) for data storage, exchange, serialization, database, etc.
if (null == firstInstant) {
firstInstant = instant; // Capture the first instant.
}
Duration duration = Duration.between(firstInstant, instant);
Long deltaInSeconds = duration.getSeconds();
double doubleDeltaInSeconds = deltaInSeconds.doubleValue();
timeVals.add(doubleDeltaInSeconds);
priceVals.add(price);
//System.out.println("deltaInSeconds: " + deltaInSeconds + " | price: " + price + " | index: " + index);
}
Double [] timeValsArray = timeVals.toArray(new Double[timeVals.size()]);
Double [] priceValsArray = timeVals.toArray(new Double[priceVals.size()]);
Double[] timeFeed = new Double[timeVals.size()];
Double[] priceFeed = new Double[priceVals.size()];
for(int x = 0;x<timeVals.size(); x++) {
timeFeed[x] = new Double (timeValsArray[x].doubleValue());
priceFeed[x] = new Double (priceValsArray[x]);
}
PolynomialFunctionLagrangeForm pflf = new PolynomialFunctionLagrangeForm(timeFeed,priceFeed);
}

According to the documentation, the PolynomialFunctionLagrangeForm constructor takes two double[] arrays, not Double[].
Hence you need to create a raw array and pass that:
...
double[] timeFeed = new double[timeVals.size()];
double[] priceFeed = new double[priceVals.size()];
for(int x = 0; x < timeVals.size(); x++) {
timeFeed[x] = timeValsArray[x].doubleValue();
priceFeed[x] = priceValsArray[x].doubleValue();
}
...
See also How to convert an ArrayList containing Integers to primitive int array? for some alternative ways to convert an ArrayList<T> (where T is a wrapper for a primitive type) to the corresponding raw array T[].
Note that there is also obviously a typo in your code:
Double [] priceValsArray = timeVals.toArray(new Double[priceVals.size()]);
needs to be
Double [] priceValsArray = priceVals.toArray(new Double[priceVals.size()]);

Java - Improving iteration through large String List

I have to parse files which has around 50000 lines and has to iterate through each line, parse, create a List and save to database. Initially I thought the time taken is because of reading the file. But the file is actually read within a second. But the parsing of data takes long time.
public static final String record = "dlrCode,partNumber,5,0.00,5000.00,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0,0.00,0";
public static final String COMMA = ",";
public static final String QUOTES = "\"";
public static final String EMPTY_STRING = "";
public static void main(String[] args){
List<String> recordsList = new ArrayList<String>();
Date time = new Date();
Part partVO = null;
PartHistory partHistoryVO = null;
List<PartHistory> partHistoryList = null;
List<Part> partsList = new ArrayList<Part>();
int splitLength = 0;
Calendar cal = Calendar.getInstance();
int historySplitCount = 0;
int monthCountReverse = 0;
//add 20000 records to list
for(int i=0; i<20000; i++){
recordsList.add(record);
}
System.out.println("Added in "+((new Date()).getTime() - time.getTime()) +" ms");
//reset time
time = new Date();
//parse records
for(String sCurrentLine : recordsList){
partVO = new Part();
partHistoryList = new ArrayList<PartHistory>();
//Parsing inventory information
partVO.setDealerCode(sCurrentLine.split(COMMA)[0]);
partVO.setPartNumber(sCurrentLine.split(COMMA)[1]);
partVO.setDmsMfId(sCurrentLine.split(COMMA)[2]);
partVO.setQtyOnHand(Math.round(Float.parseFloat(sCurrentLine.split(COMMA)[3])));
partVO.setDealerNet(Float.parseFloat(sCurrentLine.split(COMMA)[4]));
//Parsing history information
//starting from the 6th record as the first 5 records are used above
historySplitCount = 5;
//to subtract one month from current date
monthCountReverse = -1;
splitLength = sCurrentLine.split(COMMA).length;
while(splitLength>=(historySplitCount+1)){
partHistoryVO = new PartHistory();
//subtract one month from current date
cal.add(Calendar.MONTH, monthCountReverse);
partHistoryVO.setMonth(cal.get(Calendar.MONTH)+1);
partHistoryVO.setYear(cal.get(Calendar.YEAR));
partHistoryVO.setLineHitsMonthly(Math.round(Float.parseFloat(sCurrentLine.split(COMMA)[historySplitCount])));
historySplitCount++;
partHistoryVO.setQuantity(Math.round(Float.parseFloat(sCurrentLine.split(COMMA)[historySplitCount])));
historySplitCount++;
partHistoryList.add(partHistoryVO);
}
partVO.setHistoryList(partHistoryList);
partsList.add(partVO);
}
System.out.println("Iterated in "+((new Date()).getTime() - time.getTime()) +" ms");
}
Output
Added in 15 ms
Iterated in 12823 ms
Can the iteration time be improved and brought under atleast 5 seconds?

You're calling
sCurrentLine.split(COMMA)
several times in your code. Make a
final String[]
variable the first time you call it in the loop and use that instead thereafter and it'll get that many times faster.

For each line, you call the split() function multiple times, sCurrentLine.split(COMMA)[0],
a better way is to split it once and store into an array
String[] elements = sCurrentLine.split(COMMA);
dealerCode = elements[0];
partNumber = elements[1];
FYI, to count how much time spent, you can also use System.currentTimeMillis(), this does not need to create a new Date instance :)
long timeStarts = System.currentTimeMillis();
//loop goes here
long timeTook = System.currentTimeMillis() - timeStarts;

How to find the difference of two timestamps in java?

I have an ArrayList including several number of time-stamps and the aim is finding the difference of the first and the last elements of the ArrayList.
String a = ArrayList.get(0);
String b = ArrayList.get(ArrayList.size()-1);
long diff = b.getTime() - a.getTime();
I also converted the types to int but still it gives me an error The method getTime is undefined for the type String.
Additional info :
I have a class A which includes
String timeStamp = new SimpleDateFormat("ss S").format(new Date());
and there is a class B which has a method private void dialogDuration(String timeStamp)
and dialogueDuration method includes:
String a = timeSt.get(0); // timeSt is an ArrayList which includes all the timeStamps
String b = timeSt.get(timeSt.size()-1); // This method aims finding the difference of the first and the last elements(timestamps) of the ArrayList (in seconds)
long i = Long.parseLong(a);
long j = Long.parseLong(b);
long diff = j.getTime()- i.getTime();
System.out.println("a: " +i);
System.out.println("b: " +j);
And one condition is that the statement(String timeStamp = new SimpleDateFormat("ss S").format(new Date());) wont be changed in class A. And an object of class B is created in class A so that it invokes the dialogueDuration(timeStamp) method and passes the values of time-stamps to class B.
My problem is this subtraction does not work, it gives an error cannot invoke getTime() method on the primitive type long. It gives the same kind of error also for int and String types?
Thanks a lot in advance!

Maybe like this:
SimpleDateFormat dateFormat = new SimpleDateFormat("ss S");
Date firstParsedDate = dateFormat.parse(a);
Date secondParsedDate = dateFormat.parse(b);
long diff = secondParsedDate.getTime() - firstParsedDate.getTime();

Assuming you have Timestamp objects or Date Objects in your ArrayList you could do:
Timestamp a = timeSt.get(0);
Timestamp b = timeSt.get(timeSt.size()-1);
long diff = b.getTime() - a.getTime();

You can calculate the difference with the both following methods(also you can modify the mentioned methods to return difference as 'millisecond', 'day', 'month', etc by adding additional if statement or using switch case):
private Long calculateDifference(String date1, String date2, String value) {
Timestamp date_1 = stringToTimestamp(date1);
Timestamp date_2 = stringToTimestamp(date2);
long milliseconds = date_1.getTime() - date_2.getTime();
if (value.equals("second"))
return milliseconds / 1000;
if (value.equals("minute"))
return milliseconds / 1000 / 60;
if (value.equals("hours"))
return milliseconds / 1000 / 3600;
else
return new Long(999999999);
}
private Timestamp stringToTimestamp(String date) {
try {
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date parsedDate = dateFormat.parse(date);
return new Timestamp(parsedDate.getTime());
} catch (Exception e) {
return null;
}
}
For example:
calculateDifference("2021-10-20 10:00:01", "2021-10-20 10:15:01", "minute");
will return '-15'
or
calculateDifference("2021-10-20 12:00:01", "2021-10-20 10:15:01", "minute");
will return '105'

You should make your ArrayList x to an ArrayList<TimeStamp> x. Subsequently, your method get(int) will return an object of type TimeStamp (instead of a type String). On a TimeStamp you are allowed to invoke getTime().
By the way, do you really need java.sql.TimeStamp? Maybe a simple Date or Calendar is easier and more appropriate.

Logic Problem - Java

I have a family tree app which allows you to build nodes. I am stuck on a problem which requires editing a members date of birth. The date of birth is just a string in the following format dd-mm-yyyy. My problem arises when checking if the date of birth is valid (i.e. any parent cannot be younger than a child). So if the node has both parents and children and user selects to edit it's date of birth, the function must continuously check to see whether an age between the two dates has been added. The problem I am having is getting this continual check to occur using the methods I have defined. I'm hoping someone understands the isue and can help. Note checkDOb also sets the dob too. its bad naming on my part.
here is the code:
private void dateCheck(FamilyMember node) {
String dob = enterDateOfBirth();
if (node.hasChildren()) {
node.setDob(dob);
checkDob(node, node.getOldestChild(), 0);
}
FamilyMember parent = null;
if (node.hasMother() && node.hasFather()) {
if (node.getMother().getAge() > node.getFather().getAge()) {
parent = node.getFather();
} else {
parent = node.getMother();
}
checkDob(parent, node, 1);
} else {
//single parent
if (node.hasMother()) {
parent = node.getMother();
checkDob(parent, node, 1);
}
if (node.hasFather()) {
parent = node.getFather();
checkDob(parent, node, 1);
}
}
}
private void checkDob(FamilyMember parent, FamilyMember child, int member) {
out.println(parent.getYear());
out.println(child.getYear());
while (parent.getYear() > child.getYear()) {
out.println("Invalid Date - The Oldest Child of " + parent.getFullName()
+ "(" + child.getFullName() + ")\n cannot older than his/her parents. Try Again.");
out.println();
if (member == 0) {
parent.setDob(enterDateOfBirth());
}
if (member == 1) {
child.setDob(enterDateOfBirth());
}
}
}
private String enterDateOfBirth() {
out.print("Enter Year Of Birth (0 - 2011): ");
String y = in.nextLine();
out.print("Enter Month Of Birth (1-12): ");
String m = in.nextLine();
if (m.trim().equals("")) {
m = "0";
}
if (m.length() == 1) {
m = "0" + m;
}
m += "-";
out.print("Enter Date of Birth (1-31): ");
String d = in.nextLine();
if (d.trim().equals("")) {
d = "0";
}
if (d.length() == 1) {
d = "0" + d;
}
d += "-";
String dob = d + m + y;
while (!DateValidator.isValid(dob)) {
out.println("Invalid date. Try again.");
dob = enterDateOfBirth();
}
return (dob);
}
Thanks in advance.

Well the standard way to parse Dates is using SimpleDateFormat. But I don't think that will help in your case you so I won't go there.
But you should use Date objects (or, as others will say: use JodaTime's DateTime object) when you are talking about Dates, it makes things easier.
make Date the type of dob
and exchange this code:
String dob = d + m + y;
for this:
Calendar cal = Calendar.getInstance();
cal.set(Calendar.YEAR, Integer.parseInt(y));
cal.set(Calendar.MONTH, Integer.parseInt(m)-1);
cal.set(Calendar.DATE, Integer.parseInt(d));
Date dob = cal.getTime();
(you should lose all the if (m.length() == 1) stuff, because Strings with leading zeroes will be parsed as octal values)
Now you can just validate that parentBirthDate.compareTo(childBirthDate)>0
Also, to be more precise you should truncate all the fields that are smaller than day:
cal.set(Calendar.HOUR, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
Also: don't use System.out.println(), use a logging framework like Log4J or SLF4J.
Oh, BTW, validating that the child is younger than the parent won't be enough. You will probably have to validate that the difference is 12 years or more :-)

It can be smt like
//return true if one of arguments is true!
private boolean bornBefore(FamilyMember first, FamilyMember second){
if(first == null || second == null){
return true;
}
return /*your magic date comaparator*/;
}
private boolean validDate(FamilyMember node, MagicDate date) {
return bornBefore(node, node.getOldestChild())
&& bornBefore(node.getFather(), node)
&& bornBefore(node.getMother(), node);
}
}

You should decouple your validation and data entry. To start of you have your tree model with the current values and a new string that you want to enter in to change a value.
bool checkDOB(String date, FamilyMember node) {
//return true if date is more recent than any parents of node and
//older than any children of node
}
Now that you have a stand alone validation method, you should call it anytime you are about to add a new node or edit one. Do not change any values in the actual data model until it has been validated This means your tree will always be in a valid state and an edit is just a local operation.