what is this "it <= ' '" in trim string function mean here

Question

I have this Java code to trim a string

String title = titleEt.getText().toString().trim();

When I convert to kotlin, I expect this should be the kotlin code to trim the leading and trailing spaces.

val title = titleEt.text.toString().trim()

However, the IDE generates this code

val title = titleEt.text.toString().trim { it <= ' ' }

What is this { it <= ' ' } here? Is it any char less and than ' '?

Answer 1

Java's String#trim() removes all codepoints between '\u0000' (NUL) and '\u0020' (SPACE) from the start and end of the string.

Kotlin's CharSequence.trim() removes only leading and trailing whitespace by default (characters matching Char.isWhitespace, which is Character#isWhitespace(char)). For the same behavior as Java, the IDE generated a predicate that matches the same characters that Java would have trimmed.

These characters include ASCII whitespace, but also include control characters.

'\u0000' ␀ ('\0')
'\u0001' ␁
'\u0002' ␂
'\u0003' ␃
'\u0004' ␄
'\u0005' ␅
'\u0006' ␆
'\u0007' ␇ ('\a')
'\u0008' ␈ ('\b')
'\u0009' ␉ ('\t')
'\u000A' ␊ ('\n')
'\u000B' ␋ ('\v')
'\u000C' ␌ ('\f')
'\u000D' ␍ ('\r')
'\u000E' ␎
'\u000F' ␏
'\u0010' ␐
'\u0011' ␑
'\u0012' ␒
'\u0013' ␓
'\u0014' ␔
'\u0015' ␕
'\u0016' ␖
'\u0017' ␗
'\u0018' ␘
'\u0019' ␙
'\u001A' ␚
'\u001B' ␛
'\u001C' ␜
'\u001D' ␝
'\u001E' ␞
'\u001F' ␟
'\u0020' ␠ (' ')