KOTLIN / JAVA: String doesn't get replaced in a loop

Question

val string = "8% of 25 is the same as <img src=\"/someimage.png\" class=\"limit\">There are no heroes in a punk rock band <img src=\"/someimage.png\" class=\"limit\">"

val arraySearchInTheStringVariableAbove = arrayOf(
    "<img src=\"/someimage.png\" class=\"limit\">", 
    "<img src=\"/someimage.png\" class=\"limit\">"
)

val arrayReplacementInTheStringVariableAbove = arrayOf(
    "<img src=\"/someimage.png\" class=\"another-limit\" data-id=\"1\">", 
    "<img src=\"/someimage.png\" class=\"another-limit\" data-id=\"2\">"
)

arraySearchInTheStringVariableAbove.forEachIndexed { index, it ->
    string.replace(it, arrayReplacementInTheStringVariableAbove[index])
}

println(string)

the string doesn't get replaced. still shows:

8% of 25 is the same as <img src="/someimage.png" class="limit">There are no heroes in a punk rock band <img src="/someimage.png" class="limit">

where it should have been

8% of 25 is the same as <img src="/someimage.png" class="another-limit" data-id="1">There are no heroes in a punk rock band <img src="/someimage.png" class="another-limit" data-id="2">

notice the <img> tag gets replaced sequentially

String is immutable, so replace doesn't modify the object its called on, but returns a new modified one instead. You ignore that return value, effectively making the whole method call pointless. — Joachim Sauer
– Joachim Sauer, Commented Feb 24, 2021 at 13:59
To make this work you'd need to put the new string created by replace into the array. — mrmcgreg
– mrmcgreg, Commented Feb 24, 2021 at 14:00

laalto · Accepted Answer · 2021-02-24 13:59:37Z

4

Java and Kotlin strings are immutable and not editable in place. replace() returns a new string that you're throwing away.

One way to fix that is change the val string to a var string and assign the returned string back to it.

answered Feb 24, 2021 at 13:59

laalto

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Comments

Rajan Kali · Accepted Answer · 2021-02-24 14:01:35Z

3

String is immutable, every time you transform it, it creates new String in StringPool, you can assign it back to same string as var

var string = "8% of 25 is the same as <img src=\"/someimage.png\" class=\"limit\">There are no heroes in a punk rock band <img src=\"/someimage.png\" class=\"limit\">"

val arraySearchInTheStringVariableAbove = arrayOf(
    "<img src=\"/someimage.png\" class=\"limit\">", 
    "<img src=\"/someimage.png\" class=\"limit\">"
)

val arrayReplacementInTheStringVariableAbove = arrayOf(
    "<img src=\"/someimage.png\" class=\"another-limit\" data-id=\"1\">", 
    "<img src=\"/someimage.png\" class=\"another-limit\" data-id=\"2\">"
)

arraySearchInTheStringVariableAbove.forEachIndexed { index, it ->
    string = string.replace(it, arrayReplacementInTheStringVariableAbove[index])
}

println(string)

answered Feb 24, 2021 at 14:01

Rajan Kali

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3 Comments

mending3 Over a year ago

tried with listOf. I notice weird behavior when the data-id value is always 1. this the code: pastebin.com/jDm7U6ic .

mending3 Over a year ago

8% of 25 is the same as <img src="/someimage.png" class="another-limit" data-id="1">There are no heroes in a punk rock band <img src="/someimage.png" class="another-limit" data-id="1">

. notice the data-id value

Rajan Kali Over a year ago

use replaceFirst instead, because replace replaces all occurences

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