question: public static String unicodeEscape ( String s ) { if ( allAscii ( s ) ) { return s ; } StringBuilder sb = new StringBuilder ( s . length ( ) ) ; int len = s . length ( ) ; for ( int i = 0 ; i < len ; ++ i ) { char ch = s . charAt ( i ) ; if ( ch <= 127 ) { sb . append ( ch ) ; } else { sb . append ( "\\u" ) ; String hexString = Integer . toHexString ( ch ) ; int numZerosToPad = 4 - hexString . length ( ) ; for ( int j = 0 ; j < numZerosToPad ; ++ j ) { sb . append ( '0' ) ; } sb . append ( hexString ) ; } } return sb . toString ( ) ; }
target:  Replaces each non-ascii character in s with its Unicode escape sequence \\uxxxx where xxxx is a hex number. Existing escape sequences won't be affected.