What is the purpose of these interfaces?
CharSequence is a standard Java interface representing a sequence of characters. String is the most commonly-used concrete implementation of CharSequence, followed by StringBuilder.
Spanned is a CharSequence with “spans” indicating formatting to apply to portions of the text, where those spans cannot be modified.
Spannable is a Spanned, adding in the ability to modify the spans (to add or remove formatting), but not to modify the text itself.
SpannedString is a concrete implementation of the Spanned interface.
SpannableString is a concrete implementation of the Spannable interface.
in which scenarios is it mostly common to use them?
When there is a method that returns one (e.g., getText() on an EditText) or when there is a method that takes one as a parameter (e.g., setText() on a TextView).
Your cited case of using Html.fromHtml() is perhaps the most common in conventional Android development, as a TextView with a Spanned is much lighter in weight than is a WebView. However, there are other use cases, such as:
-
Allowing users to enter in rich text, then using
Html.toHtml()to persist that formatted text in an HTML rendition
In which cases is it best to avoid using them?
They are singularly awful at combating baldness, snow removal, heat pump repair, making a soufflé, etc.
🙂
Are there any obvious performance impacts to be considered when using any one of them?
Interfaces, by definition, do not have “performance impacts” — they are merely a description of an API.
I am not aware that SpannableString is significantly slower than SpannedString at any particular operation. However, SpannableStringBuilder (which allows for manipulating the text in addition to the spans that format that text) may well be a bit slower than SpannableString or SpannedString for various things. Whether or not the performance differences are enough to matter will depend on usage, though.