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Long values are concatenating instead of adding

I have this method:
public NumPal next(){
stringRev = reverseString(stringCur);
numRev = Long.parseLong(stringRev);
numCur = Long.parseLong(stringCur);
numCur = (numCur + numRev);
stringCur = Long.toString(numCur);
NumPal n = new NumPal(stringCur);
return n;
}
When i try to add numCur and numRev it for some reason concatenates them. Are they staying as strings? I believe I'm using Long.ParseLong correctly but im not sure.

Check whether the addition is overflowing long size. long size range is 2^63 to 2^63–1. If you want to addition of big numbers which cannot be accommodated in long, try the method present in this link. https://www.geeksforgeeks.org/sum-two-large-numbers/

Converting large scientific number to long

I've spend a long time now, trying to convert the number 1.2846202978398e+19 in java, without any luck. Currently what I'm trying to do (long)Double.parseDouble(hashes), however this gives 9223372036854775807, which is obviously incorrect. The actual number should look something like this 12855103593745000000.
Using int val = new BigDecimal(stringValue).intValue(); returns -134589568 as it's unable to hold the result. Switching the code to long val = new BigDecimal(hashes).longValue(); gives me -5600541095311551616 which is also incorrect.
I'm assuming this is happening due to the size of a double compared to a long.
Any ideas?

Did you try to use String.format :
String result = String.format("%.0f", Double.parseDouble("1.2846202978398e+19"));
System.out.println(result);
Output
12846202978398000000
Edit
Why you don't work with BigDecimal to do the arithmetic operations, for example :
String str = "1.2846202978398e+19";
BigDecimal d = new BigDecimal(str).multiply(BigDecimal.TEN);
// ^^^^^^^^------example of arithmetic operations
System.out.println(String.format("%.0f", d));
System.out.println(String.format("%.0f", Double.parseDouble(str)));
Output
128462029783980000000
12846202978398000000

Your value exceeds the maximum size of long. You can not use long in this situation.
Try
BigDecimal value = new BigDecimal("1.2846202978398e+19");
After that, you can call
value.toBigInteger()
or
value.toBigIntegerExact()
if needed.

What about:
System.out.println(new BigDecimal("1.2846202978398e+19").toBigInteger());

Code crashing after using formatting

I'm new to the Java language (Just started about 2 weeks ago)
Basically, the user enters their year/month/day they were born on in order and I use this information to perform a math calculation that will show their age.
I need numbers from 0-9 to be taken in as 01, 02, 03... So, I searched around and found that I can use Decimal.Format and then print out the format later on.
My code crashes whenever it reaches the println(twodigits.format) part no mater where I put it. There are no errors displayed that I need to address.
Why is it doing this and is there a better way to do this? I need it to be 2 digits at all times or the calculation won't work.
Here's a part of my code, I can provide more if needed.
DecimalFormat twodigits = new DecimalFormat("00");
System.out.println("Calculating...");
Integer CurrentDate2 = Integer.valueOf(CurrentDate);
Integer BirthDate2 = Integer.valueOf(BirthDate);
int a = CurrentDate2.intValue();
int b = BirthDate2.intValue();
int age = (a - b) / 1000;
Thread.sleep(300);
System.out.println(".");
Thread.sleep(300);
System.out.println(".");
Thread.sleep(300);
System.out.println(".");
System.out.println(twodigits.format(CurrentDate));
System.out.println(twodigits.format(BirthDate));
Any help is appreciated!

What types are "CurrentDate" and "BirthDate" because it's not clear from your code? You first use them to set "CurrentDate2" and "BirthDate2". And then you use them in the println().
If I were to guess, I'd say they are of type 'String', and 'twodigits.format()' can't handle Strings, which is why it's crashing.

This takes two dates and split time on "/". It then prints them out in the format that you want.
DecimalFormat twodigits = new DecimalFormat("00");
System.out.println("Calculating...");
String CurrentDate = "01/02/2007";
String BirthDate = "02/03/2007";
String[] currentDateParts = CurrentDate.split("/");
String[] birthDateParts = BirthDate.split("/");
int cdp0 = Integer.parseInt(currentDateParts[0]);
int cdp1 = Integer.parseInt(currentDateParts[1]);
int cdp2 = Integer.parseInt(currentDateParts[2]);
int bdp0 = Integer.parseInt(birthDateParts[0]);
int bdp1 = Integer.parseInt(birthDateParts[1]);
int bdp2 = Integer.parseInt(birthDateParts[2]);
//do your calculations
System.out.println(twodigits.format(cdp0));
System.out.println(twodigits.format(cdp1));
System.out.println(twodigits.format(cdp2));
System.out.println(twodigits.format(bdp0));
System.out.println(twodigits.format(bdp1));
System.out.println(twodigits.format(bdp2));

Java BigDecimal Problems (String to BigDecimal - BigDecimal to String)

I know, there are dozens of topic like this in site but I am having trouble with 3 problems and I couldnt figure out all of them at the same time.
Actually, I am trying to make a calculator for Android but sometimes I cannot get what I am expected to.
A part of my code is;
}else if(operator.equals("/")){
if(resultScreen.indexOf("/")==0){
strNum2 = resultScreen.substring(resultScreen.indexOf("/")+1,resultScreen.length());
intNum1 = result;
}else{
strNum1 = resultScreen.substring(0,resultScreen.indexOf("/"));
strNum2 = resultScreen.substring(resultScreen.indexOf("/")+1,resultScreen.length());
intNum1 = new BigDecimal(strNum1);
}
intNum2 = new BigDecimal(strNum2);
if(intNum2.equals(0)){
tvScreen.setText("Err");
resultScreen ="";
}else{
result = intNum1.divide(intNum2);
resultScreen = result.toString();
tvScreen.setText(resultScreen);
resultScreen ="";
}
}
When I try to;
22/7
It comes up;
3
How can I fix that?
By the way, I want to keep the exact value of decimal.

This works
BigDecimal a = new BigDecimal("22");
BigDecimal b = new BigDecimal("3");
BigDecimal res = a.divide(b, 2, RoundingMode.HALF_UP);
System.out.println(res);
The key thing is to have a roundingMode else if the value can not be represented exactly an Exception will be thrown.

Java convert float to integer

I want to do an operation like this : if the given float numbers are like 1.0 , 2.0 , 3.0 , I want to save them to database as integer (1,2,3 ), if they are like 1.1 , 2.1 , ,3.44 , I save them as float. what's the best solution for this problem using java ? The corresponding field in database is type of varchar.

Just try int i = (int) f;.
EDIT : I see the point in the question. This code might work :
int i = (int) f;
String valToStore = (i == f) ? String.valueOf(i) : String.valueOf(f);

String result = "0";
if (floatVar == Math.floor(floatVar)) {
result = Integer.toString((int) floatVar);
} else {
result = Float.toString(floatVar);
}
The if-clause checks whether the number is a whole number - i.e. if it is equal to the result of rounding it down to the closest whole value.
But this is very odd requirement indeed, and perhaps you should reconsider the need for such a thing.

Seems like you want to save Floats with no trailing numbers as Integers, while saving those with significant trailing numbers as Floats. I would rather just save it all as Float to the DB, but it's your question so here's my answer:
/**
* Method to determine if trailing numbers are significant or not. Significant
* here means larger than 0
*
* #param fFloat
* #return
*/
public static boolean isTrailingSignificant(Float fFloat)
{
int iConvertedFloat = fFloat.intValue();// this drops trailing numbers
// checks if difference is 0
return ((fFloat - iConvertedFloat) > 0);
}
This is how you would use this method:
Number oNumToSave = null;
if (isTrailingSignificant(fFloat))
{
// save float value as is
oNumToSave = fFloat;
}
else
{
// save as int
oNumToSave = fFloat.intValue();// drops trailing numbers
}
After that, you can do the database operation using the variable oNumToSave.

Not sure this is the best solution, but you can try to write a method like this :
String convertToString(Float f) {
if (f.toString().endsWith(".0"))
return f.intValue().toString();
else
return f.toString();
}

Kotlin:
val mAmount = 3.0
val intAmount = mAmount.toInt()
val amountToDisplay = if (intAmount.compareTo(mAmount) == 0) intAmount.toString() else java.lang.String.valueOf(mAmount)