How to use string property correctly in Kotlin?

Question

I have the following code which will call function save() based on the first five characters of the string in the EditText. What I am trying to save to the database is anything after the first five characters in the edit text, if the condition is met.

Below code works fine when the string in the edit text is more than five characters. If the length of the string is less than 5 then the app crashes. In order to avoid this, I added the second block of code to find the length of the string but it does not work. Can you check where is the issue?

 val pass =findViewById<EditText>(R.id.editText).text.toString()
            var password: String = pass.substring(0,5)

            if (password == "hello"){
                save()
                Toast.makeText(this, "Database updated", Toast.LENGTH_LONG).show()
            }
            else
            {
                Toast.makeText(this, "Unauthorized user", Toast.LENGTH_LONG).show()
            }

        }

I tried the following code in the REPL and it returned, following lines or error.

java.lang.StringIndexOutOfBoundsException: String index out of range: 3 at java.lang.String.substring(String.java:1963)

var pass="gl"
var password = pass.substring(0,3)
val len = password.length
println(len)
print(password)

When the length of the variable pass is equal to or more than 3 characters then it executes without error in REPL.

I am on Android Studio using Kotlin.

NB: The Second block of code, as is, not what is written into the editor. It's is the sample what I was trying in the REPL.

Amit Tiwary · Accepted Answer · 2020-01-02 07:04:58Z

1

First check the length of the string and then do work according to size of length like

val length = pass.length
if(length<5){
    println(len);
}else{
   var password: String = pass.substring(0,5)

        if (password == "hello"){
            save()
            Toast.makeText(this, "Database updated", Toast.LENGTH_LONG).show()
        }
        else
        {
            Toast.makeText(this, "Unauthorized user", Toast.LENGTH_LONG).show()
        }
}

edited Jan 2, 2020 at 7:04

answered Jan 1, 2020 at 16:46

Amit Tiwary

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1 Comment

user3765415 Over a year ago

It worked with a slight change. Changed pass.length() to pass.length.

Son Truong · Accepted Answer · 2020-01-02 03:22:52Z

In Java/Kotlin, a String is a sequence of characters, each character has a given index, the index is starting from 0, for example:

"Hello"

length: 5 (5 characters)
startIndex: 0
endIndex: length - 1 = 5 - 1 = 4

Character    Index
    H          0
    e          1
    l          2
    l          3
    o          4

From substring Kotlin documentation:

Returns the substring of this string starting at the startIndex and ending right before the endIndex.
fun String.substring(startIndex: Int, endIndex: Int): String

Back to your example:

"gl"

length: 2
startIndex: 0
endIndex: length - 1 = 2 - 1 = 1

Character    Index
    g          0
    l          1

pass.substring(0,3) will returns a substring at the startIndex (0) and ending right before the endIndex (endIndex - 1 = 3 - 1 = 2). But 2 is an invalid index, so the program throws IndexOutOfBoundsException and make your app crash.

You can check the length of editText before calling substring() on it.

// Define this variable in scope of class
private val PASSWORD_LENGTH_MIN = 5


val pass = findViewById<EditText>(R.id.editText).text.toString()

if (pass.length < PASSWORD_LENGTH_MIN) {
    Toast.makeText(this, "Password length too short.", Toast.LENGTH_LONG).show()
} else {
    var password: String = pass.substring(0, PASSWORD_LENGTH_MIN)

    if (password == "hello") {
        save()
        Toast.makeText(this, "Database updated", Toast.LENGTH_LONG).show()
    } else {
        Toast.makeText(this, "Unauthorized user", Toast.LENGTH_LONG).show()
    }
}

Ahmed Ali · Accepted Answer · 2020-01-01 16:51:02Z

0

in your save() function put the code below to check if the string"s length is more than 5 characters

val pass =findViewById<EditText>(R.id.editText).text.toString()

if (pass.length>5){
     var password: String = pass.substring(0,5)
          if (password == "hello"){
                save()
                Toast.makeText(this, "Database updated", Toast.LENGTH_LONG).show()
            }
            else
            {
                Toast.makeText(this, "Unauthorized user", Toast.LENGTH_LONG).show()
            }
}else{
                Toast.makeText(this, "Length is less than 5 Chars", Toast.LENGTH_LONG).show()

}

answered Jan 1, 2020 at 16:51

Ahmed Ali

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