trim and pad

Learn formatting with trim, padStart and padEnd.

trim: clean edge whitespace

trim removes leading and trailing whitespace from a string. Inner spaces are untouched. trimStart and trimEnd clean only one side.

val s = "  hello  "
println(s.trim())      // "hello"
println(s.trimStart()) // "hello  "
println(s.trimEnd())   // "  hello"

It is a good habit to trim user input before processing. Then stray spaces do not break comparisons. You can also trim specific chars: trim('*').

padStart and padEnd: pad to fixed length

padStart adds a given char to the front, padEnd to the back, until the string reaches the requested length.

val code = "5"
println(code.padStart(3, '0'))  // "005"
println(code.padEnd(3, '.'))    // "5.."

padStart is handy for fixed-width tables or sequence numbers. For example, month numbers become 01, 12. If you omit the second argument, a space is used by default.

Exercise Pad the month to two digits

Pad the string "5" to 2 characters with padStart; fill the missing char with '0'. Print the result.

Show example solution

val month = "5"
println(month.padStart(2, '0'))

Test yourself

What does " hi ".trim() return?
- " hi "
- " hi"
- "hi "
- "hi"
Show answer

"hi" — trim removes leading and trailing spaces; not inner ones.

Fill in the blank: trim only the end

val s = "  hi  "
val clean = s.____()

Show answer

val s = "  hi  "
val clean = s.trimEnd()

Match method to result

trim()

Edges cleaned
trimStart()

Only front
padStart(3, '0')

Pad zeros at front
padEnd(3, '.')

Pad dots at end

Fill in the blank: pad with zeros

val code = "5"
val padded = code.____(3, '0')

Show answer

val code = "5"
val padded = code.padStart(3, '0')

Next lesson: Summary - Advanced strings

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