Have been sitting with this for over an hour, so I have a plain textField which is meant for entering Int numbers, and then I perform filtering based on the number.
My filter function
private void fillAllListsFiltered() {
List<Trip> trips = tripHib.getAllTrips();
trips.forEach(c -> { if(c.getTime() > gt(tripTextTime) && c.getLength() > gt(tripTextLength)) tripListView.getItems().add(c);});
}
And then my "function" for parsing Int from the textField. (I understand I could just parse it in the first function as Integer.parseInt(tripTextTime.getText()), but for some reason it does not work.
private static int gt(TextField textField) {
System.out.println(textField.getText());
String text = textField.getText().trim();
return Integer.parseInt(text);
}
I have also added the trim as an extra, but it didn't really help.
the error is "NumberFormatException: For input string: "" "
Related
I've tried this 10 different ways and i can't get this to work.
I want this Kotlin code to take in a string, check each character of that string against a listOf characters, and, if it is in that list, increase a counting variable by 1, so then at the end it can check if that counting variable is high enough to pass a test. this is taken straight from Sololearn: Code Coach - Password Validator. I have completed this code successfully already in Python (https://code.sololearn.com/c0fl17IMHPfC), but in trying to convert it over to Kotlin, it doesn't seem to work. The variables don't seem to register as true when compared to the elements in the listOf.
fun main() {
var password: String = readLine()!!
var numberCount: Int = 0
var numbers: List<String> = listOf("0","1","2","3","4","5","6","7","8","9")
var specialCount: Int = 0
var specialCharacters: List<String> = listOf("!","#","#","$","%","&","*")
if (password.length < 7) {
println("Weak")
} else {
for (character in password) {
println(character)
var numberCheck = numbers.contains(character)
println(numberCheck)
if (numberCheck == true) {
numberCount += 1
}
var specialCharactersCheck = specialCharacters.contains(character)
println(specialCharactersCheck)
if (specialCharactersCheck == true) {
specialCount += 1
}
}
println(numberCount)
println(specialCount)
if (numberCount < 2) {
println("Weak")
} else if (specialCount < 2) {
println("Weak")
} else {
println("Strong")
}
}
}
When I enter an input of "letssee43$#", the result of this code is:
l
false
false
e
false
false
t
false
false
s
false
false
s
false
false
e
false
false
e
false
false
4
false
false
3
false
false
$
false
false
false
false
0
0
Weak
Type inference failed. The value of the type parameter T should be mentioned in input types (argument types, receiver type or expected type). Try to specify it explicitly.
Type inference failed. The value of the type parameter T should be mentioned in input types (argument types, receiver type or expected type). Try to specify it explicitly.
Your list is a list of Strings, but for (character in password) loops over the Chars in password. So you're trying to see if one of the Strings in your list is a specific Char, which it isn't, because they're two different types - a string with a single character in it is still a String, not a Char (that's why you're getting that type error)
There are lots of ways to do it (and there's nothing wrong with your code besides the Char/String thing!), personally I'd just do this:
var numbers = "0123456789"
var specialCharacters = "!##$%&*"
val password = "letssee43$#"
val nums = password.count { it in numbers }
val specials = password.count { it in specialCharacters }
println("nums: $nums, specials: $specials")
> nums: 2, specials: 2
count is iterating over the Chars in password and counting how many of them each character string contains. A String is treated like an array of Chars, so you can check it that way. (You could also add .toList() after the string declaration if you really want your characters stored in a list - that way it'll be a List<Char> so the lookup will still work.)
Or you could do things the way you are, and explicitly write out the listOf elements - but make them Chars instead, e.g. listOf('1') (single quotes) instead of listOf("1") (double quotes).
If you do want to search a list of strings for a match, you need to provide a String, so you need to convert your Char to one, e.g. by calling toString() on it, using a literal like "$character", etc.
edit like gidds points out below, sets are way more efficient for lookups like in or contains, so toSet() is a better idea than toList() unless you really need that ordered list for some reason. If you don't care about efficiency (like if you're not doing a lot of lookups) I'd personally just leave it as a string like in the code block up there - it's nice and simple. But if you do want to be more efficient, or if you do need a collection (like if you're matching against Strings) then a Set is ideal
I will give you another way to get the same result as you by using Extensions
fun main() {
var password: String = readln()
println("Password contain numbers amount: " + password.containNumbersAmount())
println("Password contain special characters amount: "+ password.containSpecialCharactersAmount())
println("Password Status : "+ password.validationResult())
}
fun String.containNumbersAmount() = count { it.isDigit() }
fun String.containSpecialCharactersAmount(): Int {
val specialCharacters = "!##$%&*"
return count { it in specialCharacters } }
fun String.validationResult() : String {
return when {
length < 7 -> "Weak"
containNumbersAmount() < 2 -> "Weak"
containSpecialCharactersAmount() < 2 -> "Weak"
else -> "Strong"
}
}
The problem is that your Lists contain Strings, so every time you call contains on them and pass a Char, it will always be false because a Char is not a String.
Probably, the best way to fix it is to declare Iterables of Chars to check them. Lists are Iterables, but so are ranges.
val password: String = readln()
var numberCount: Int = 0
val numbers: Iterable<Char> = '0'..'9'
var specialCount: Int = 0
val specialCharacters: List<Char> = listOf('!','#','#','$','%','&','*')
And just for your learning, there's a count function that takes a lambda argument that can make this kind of task much easier:
fun main() {
val password: String = readln()
val numbers = '0'..'9'
val specialCharacters = listOf('!','#','#','$','%','&','*')
val numberCount: Int = password.count { numbers.contains(it) }
val specialCount: Int = password.count { specialCharacters.contains(it) }
val result = when {
password.length < 7 || numberCount < 2 || specialCount < 2 -> "Weak"
else -> "Strong"
}
println(result)
}
I'm having issue trying to assign different number values to a number a Radiobuttons, to then calculate together as a total sum into a textbox, but not sure where to start, im new to C# and not understanding to well, if anyone can provide a simple example I would be grateful
So far I've come up with something like this, just to try to assing the number value but cant get it to work, and not even sure how to add them together after?
Do I need to use: int?
int Basic, Reg, Pre
{
If RadioButton1.Checked = True Then
Basic = 10;
If RadioButton1.Checked = True Then
Reg = 15;
If RadioButton1.Checked = True Then
Pre = 20;
Looks mostly like Visual Basic. Try to find a beginner's tutorial on C# on the internet.
In this case the variables may not be assigned a value in the if statements. Unlike vb, you need to explicitly assign the default values to the variables before we try to add them at the end.
In C# If is if (most statements are lowercase) and the condition (the part that evaluates to true of false) is in parentheses.
In C# the assignment operator = is different from the comparison operator == which is used in many if statements. You could write
if (radioButton1.Checked == true)
but, since .Checked evaluates to true or false you can skip the == true.
if (radioButton2.Checked)
The code
private void button1_Click(object sender, EventArgs e)
{
int Basic = 0;
int Reg = 0;
int Pre = 0;
if (radioButton1.Checked == true)
Basic = 10;
if (radioButton2.Checked)
Reg = 15;
if (radioButton3.Checked)
Pre = 20;
txtTotal.Text = (Basic + Reg + Pre).ToString();
}
One last thing. ToString requires the method invoker (). vb is lazy about this. vb also allows you to skip it for constructors but you will need it in C#.
EDIT
Users can enter anything in a text box. To keep your code from blowing up it is best to use TryParse to verify a valid number. The first parameter is the string you want to convert. The second is a variable of the appropriate type to hold the converted value. The function returns True of False depending on the success of the conversion. The exclamation mark is Not in C#. If the conversion fails we inform the user and exit the method with return. If successful we continue to the multiplication with the converted values.
private void Button2_Click(object sender, EventArgs e)
{
if (!Double.TryParse(textbox5.Text,out double txt1))
{
MessageBox.Show("Please enter a valid number in textbox 5");
return;
}
if (!Double.TryParse(textbox6.Text,out double txt2))
{
MessageBox.Show("Please enter a valid number in textbox 6");
return;
}
double sum = txt1 * txt2;
textbox7.Text = sum.ToString();
}
Is there a simple way to check if user's input is numeric? Using regexes and exceptions seems too complicated here.
fun main {
val scan = Scanner(System.`in`)
val input = scanner.nextLine()
if (!input.isNumeric) {
println("You should enter a number!")
}
}
The method mentioned above will work for a number <= approximately 4*10^18 essentially max limit of Double.
Instead of doing that since String itself is a CharSequence, you can check if all the character belong to a specific range.
val integerChars = '0'..'9'
fun isNumber(input: String): Boolean {
var dotOccurred = 0
return input.all { it in integerChars || it == '.' && dotOccurred++ < 1 }
}
fun isInteger(input: String) = input.all { it in integerChars }
fun main() {
val input = readLine()!!
println("isNumber: ${isNumber(input)}")
println("isInteger: ${isInteger(input)}")
}
Examples:
100234
isNumber: true
isInteger: true
235.22
isNumber: true
isInteger: false
102948012120948129049012849102841209849018
isNumber: true
isInteger: true
a
isNumber: false
isInteger: false
Its efficient as well, there's no memory allocations and returns as soon as any non-satisfying condition is found.
You can also include check for negative numbers by just changing the logic if hyphen is first letter you can apply the condition for subSequence(1, length) skipping the first character.
joining all the useful comments and putting it in a input stream context, you can use this for example:
fun readLn() = readLine()!!
fun readNumericOnly() {
println("Enter a number")
readLn().toDoubleOrNull()?.let { userInputAsDouble ->
println("user input as a Double $userInputAsDouble")
println("user input as an Int ${userInputAsDouble.toInt()}")
} ?: print("Not a number")
}
readNumericOnly()
for input: 10
user input as a Double 10.0
user input as an Int 10
for input: 0.1
user input as a Double 0.1
user input as an Int 0
for input: "word"
Not a number
Simply use : text.isDigitsOnly() in kotlin.
Well all the answers here are best suited for their own scenarios:
But not all string are numeric digits it can have (-) and (.) decimal pointers.
So to accomplish this I made a cocktail of all the answers suggested below and from other posts as well which - looks like below :
fun isPosOrNegNumber(s: String?) : Boolean {
return if (s.isNullOrEmpty()) false
else{
if(s.first()=='-' && s.filter { it == '.' }.count() <= 1) {
s.removeRange(0,1).replace(".","").all{Character.isDigit(it)}
}
else s.all {Character.isDigit(it)}
}
}
Above code does a good job for its purpose.
But then it struck me kotlin does an even better job with matching a regex and voila the solution became simple and elegant as below :
fun isPosOrNegNumber(s: String?) : Boolean {
val regex = """^(-)?[0-9]{0,}((\.){1}[0-9]{1,}){0,1}$""".toRegex()
return if (s.isNullOrEmpty()) false
else regex.matches(s)
}
This sample regex is only for US number formats but if you want to use EU number formats then just replace '.' with ','
Bdw. if the numbers contain commas then just replace it while sending to this method or better form a regex pattern with commas in it.
Another way to check if the given string is numeric( to check for both negative and positive values ) or not:
val intChars = '0'..'9'
fun isNumeric(input: String) = input
.removePrefix("-")
.all { it in '0'..'9' }
A simple answer without any custom functions is to utilise toDoubleOrNull function. If it returns null, the string is not numeric.
val string = "-12345.666"
if (string.toDoubleOrNull()!=null) // string is numeric
{
//do something
}
If you know the input only contains integers you can also use toIntOrNull likewise
I am currently learning kotlin and therefore following the kotlin track on exercism. The following exercise required me to calculate the Hamming difference between two Strings (so basically just counting the number of differences).
I got to the solution with the following code:
object Hamming {
fun compute(dnaOne: String, dnaTwo: String): Int {
if (dnaOne.length != dnaTwo.length) throw IllegalArgumentException("left and right strands must be of equal length.")
var counter = 0
for ((index, letter) in dnaOne.toCharArray().withIndex()) {
if (letter != dnaTwo.toCharArray()[index]) {
counter++
}
}
return counter
}
}
however, in the beginning I tried to do dnaOne.split("").withIndex() instead of dnaOne.toCharArray().withIndex() which did not work, it would literally stop after the first iteration and the following example
Hamming.compute("GGACGGATTCTG", "AGGACGGATTCT") would return 1 instead of the correct integer 9 (which only gets returned when using toCharArray)
I would appreciate any explanation
I was able to simplify this by using the built-in CharSequence.zip function because StringimplementsCharSequence` in Kotlin.
According to the documentation for zip:
Returns a list of pairs built from the characters of this and the [other] char sequences with the same index
The returned list has length of the shortest char sequence.
Which means we will get a List<Pair<Char,Char>> back (a list of pairs of letters in the same positions). Now that we have this, we can use Iterable.count to determine how many of them are different.
I implemented this as an extension function on String rather than in an object:
fun String.hamming(other: String): Int =
if(this.length != other.length) {
throw IllegalArgumentException("String lengths must match")
} else {
this.zip(other).count { it.first != it.second }
}
This also becomes a single expression now.
And to call this:
val ham = "GGACGGATTCTG".hamming("AGGACGGATTCT")
println("Hamming distance: $ham")
I was solving a problem on codeforces in which I had to sum up the digits of a big number (it can have up to 100k digits) and I'd have to repeat that process until there is only one digit left and count the number of times I did that and I came up with a working solution, however I'd like to know if some things could have been done in a more "Kotlin-ish like way", so given:
fun main(args: Array<String>) {
println(transform(readLine()!!))
}
fun transform(n: String): Int {
var count = 0
var sum : Int
var s = n
while(s.length > 1) {
sum = (0 until s.length).sumBy { s[it].toInt() - '0'.toInt() }
s = sum.toString()
count++
}
return count
}
sum = (0 until s.length).sumBy { s[it].toInt() - '0'.toInt() } is there a way to I guess map the sum of digits in the string to the sum variable, or in general a better approach than the one I used?
When converting a Char to an Int it converts it to the ASCII value so I had to add "-'0'.toInt()" is there a faster way (not that it's too much to write, asking out of curiosity)?
How to make the String n mutable without creating a new String s and manipulating it? Or is that the desired (and only) way?
P.S. I'm a beginner with Kotlin.
When converting a Char to an Int it converts it to the ASCII value so I had to add "-'0'.toInt()" is there a faster way (not that it's too much to write, asking out of curiosity)?
You can simply write s[it] - '0', because subtracting Chars in Kotlin already gives you an Int:
public class Char ... {
...
/** Subtracts the other Char value from this value resulting an Int. */
public operator fun minus(other: Char): Int
...
}
But why are looping over the indexes when you could loop over the Chars directly?
sum = s.sumBy { it - '0' }
This is a functional (and recursive) style to solve it:
private fun sum(num: String, count: Int) : Int {
return num
//digit to int
.map { "$it".toInt() }
//sum digits
.sum()
//sum to string
.toString()
//if sum's length is more than one, do it again with incremented count. Otherwise, return the current count
.let { if (it.length > 1) sum(it, count + 1) else count }
}
And you call it like this:
val number = "2937649827364918308623946..." //and so on
val count = sum(number, 0)
Hope it helps!