無法訪問在接口中聲明的變量，即使它在另一個類中實現

Question

我有一個名爲StringInput的接口，其代碼如下。

public static ArrayList<String[]> fileInput() throws IOException { 
    ArrayList<String[]> lines = new ArrayList<>(); 
    try (BufferedReader br = new BufferedReader(new FileReader(file))) { 
     String line; 
     while ((line = br.readLine()) != null) { 
      String[] formatted = format(line); 
      lines.add(formatted); 
      System.out.println(line); 
     } 

    } 
    return lines; 
} 

public static String[] format(String s) { 
    String[] data = new String[9]; 
    String logEntryPattern = "^([\\d.]+) (\\S+) (\\S+) \\[([\\w:/]+\\s[+\\-]\\d{4})\\] \"(.+?)\" (\\d{3}) (\\d+) \"([^\"]+)\" \"([^\"]+)\""; 

    System.out.println("Using RE Pattern:"); 
    System.out.println(logEntryPattern); 
    System.out.println("Combined Apache Log Format (VERBOSE)"); 

    System.out.println("Input line is:"); 
    System.out.println(s); 

    Pattern p = Pattern.compile(logEntryPattern); 
    Matcher matcher = p.matcher(s); 
    if (!matcher.matches() 
      || NUM_FIELDS != matcher.groupCount()) { 
     System.err.println("Bad log entry (or problem with RE?):"); 
     System.err.println(s); 
     return null; 
    } 

    System.out.println("IP Address: " + matcher.group(1)); 
    String clientIP = matcher.group(1); 
    System.out.println("Identd: " + matcher.group(2)); 
    String identd = matcher.group(2); 
    System.out.println("UserID: " + matcher.group(3)); 
    String userID = matcher.group(3); 
    System.out.println("Date&Time: " + matcher.group(4)); 
    String dateTime = matcher.group(4); 
    System.out.println("Request: " + matcher.group(5)); 
    String protocol = matcher.group(5); 
    System.out.println("Response: " + matcher.group(6)); 
    String respCode = matcher.group(6); 
    System.out.println("Bytes Sent: " + matcher.group(7)); 
    String respSize = matcher.group(7); 
    System.out.println("Referer: " + matcher.group(8)); 
    String refer = matcher.group(8); 
    System.out.println("Browser: " + matcher.group(9)); 
    String userAgent = matcher.group(9); 
    data[0] = clientIP; 
    data[1] = identd; 
    data[2] = userID; 
    data[3] = dateTime; 
    data[4] = protocol; 
    data[5] = respCode; 
    data[6] = respSize; 
    data[7] = refer; 
    data[8] = userAgent; 
    return data; 
} 

和另一個名爲ParseUpload的類實現了接口幷包含一個main方法。在main方法裏面，我有一個準備好的語句試圖從接口調用一個變量。但是，我不能。我不知道，因爲我通常不使用接口，沒有實例化它對我來說很奇怪。 有什麼幫助嗎？謝謝。

編輯：這是另一類。

public class ParseUpload implements StringInput { 

public static void main(String argv[]) { 

    try { 
     StringInput.fileInput(); 

    } catch (Exception e) { 
     e.printStackTrace(); 
    } 

    //while (logEntryLine !=null){ 
    // for (int i = 0; i < file.length(); i++){ 
    //System.out.println(fileExists); ignore/For testing purposes 
    Connection conn = null; 

    try { 
     Class.forName("com.mysql.jdbc.Driver"); 
     Connection con = DriverManager.getConnection("jdbc:mysql://localhost:5294/mysql", "root", "Iu&#KR489)("); 
     System.out.println("Database Connection Established!"); 

     String query = " insert into alogs(clientIP, identd, userID, dateTime, protocol, respCode, respSize, refer, userAgent)" 
       + " values (?, ?, ?, ? ,? ,? ,?, ?, ?)"; 

     PreparedStatement preparedStmt = con.prepareStatement(query); 
     preparedStmt.setString(1, data); 
     preparedStmt.setString(2, identd); 
     preparedStmt.setString(3, userID); 
     preparedStmt.setString(4, dateTime); 
     preparedStmt.setString(5, protocol); 
     preparedStmt.setString(6, respCode); 
     preparedStmt.setString(7, respSize); 
     preparedStmt.setString(8, refer); 
     preparedStmt.setString(9, userAgent); 
     preparedStmt.execute(); 

     con.close(); 

    } catch (SQLException ex) { 
     System.out.println("****************************Can't Connect to the database***********************************"); 
     System.out.println("SQLException: " + ex.getMessage()); 
     System.out.println("SQLState: " + ex.getSQLState()); 
     System.out.println("VendorError: " + ex.getErrorCode()); 
    } catch (ClassNotFoundException e) { 
     System.out.println("Class Not Found"); 

    } 
    // } 
} 

}

Answer 1

你的問題不是一個接口問題。
你的情況，你應該有：

1. StringInput與一些靜態方法的類（這些方法將返回一個變量，你就可以使用它）
2. ParseUpload會調用這些方法，以得到結果並使用它。

下面是一個簡單的例子：

public class StringInput { 
    public static String[] format() { 
     String[] datas = new String[2]; 
     datas[0] = "Some"; 
     datas[1] = "thing"; 
     return datas; 
    } 
} 

和：

public class ParseUpload { 
    public static void main(String[] args) { 
     String[] resultOfFormatCall = StringInput.format(); 
     // Now you have the result of your format method, and you are able to use it 
     System.out.println("result[0]" + resultOfFormatCall[0] + ";result[1]" + resultOfFormatCall[1]); 
    } 
}