question: public static String previous ( CharSequence self ) { StringBuilder buffer = new StringBuilder ( self ) ; if ( buffer . length ( ) == 0 ) throw new IllegalArgumentException ( "the string is empty" ) ; char last = buffer . charAt ( buffer . length ( ) - 1 ) ; if ( last == Character . MIN_VALUE ) { buffer . deleteCharAt ( buffer . length ( ) - 1 ) ; } else { char next = last ; next -- ; buffer . setCharAt ( buffer . length ( ) - 1 , next ) ; } return buffer . toString ( ) ; }
target:  This method is called by the -- operator for the class CharSequence. It decrements the last character in the given CharSequence. If the last character in the CharSequence is Character.MIN_VALUE it will be deleted. The empty CharSequence can't be decremented.