private boolean skipSpace() {
        boolean space = false;
        while (!exp.isEmpty() && Character.isWhitespace(exp.peek())) {
            space = true;
            exp.poll();
        }
        return space;
    }
private boolean skipSpace() {
        boolean space = false;
        while (!exp.isEmpty() && Character.isWhitespace(exp.peek())) {
            space = true;
            exp.poll();
        }
        return space;
    }
private boolean skipSpace ( ) { boolean space = false ; while ( ! exp . isEmpty ( ) && Character . isWhitespace ( exp . peek ( ) ) ) { space = true ; exp . poll ( ) ; } return space ; }
跳过空格,并返回是否跳过空格(是否存在空格)
跳过空格 并返回是否跳过空格 ( 是否存在空格 )