scala> "foo".

+                     asInstanceOf          charAt                codePointAt           codePointBefore       codePointCount        compareTo             compareToIgnoreCase   concat
contains              contentEquals         endsWith              equalsIgnoreCase      getBytes              getChars              indexOf               intern                isEmpty
isInstanceOf          lastIndexOf           length                matches               offsetByCodePoints    regionMatches         replace               replaceAll            replaceFirst
split                 startsWith            subSequence           substring             toCharArray           toLowerCase           toString              toUpperCase           trim

“foo” で　タブを押すと補完される