与 J2me 读取文件的混淆。请帮助我理解

Question

我正在为 Symbian S60 手机开发 J2ME 应用程序，其中需要读取文本文件。我无法访问 BufferedReader 从文件中提取一行文本，但我确实在诺基亚帮助论坛中找到了这一点，这让我有点困惑。这是代码，我的问题如下。感谢您的回答。

    /**
     * Reads a single line using the specified reader.
     * @throws java.io.IOException if an exception occurs when reading the
     * line
     */
    private String readLine(InputStreamReader reader) throws IOException {
        // Test whether the end of file has been reached. If so, return null.
        int readChar = reader.read();
        if (readChar == -1) {
            return null;
        }
        StringBuffer string = new StringBuffer("");
        // Read until end of file or new line
        while (readChar != -1  && readChar != '\n') {
            // Append the read character to the string. Some operating systems
            // such as Microsoft Windows prepend newline character ('\n') with
            // carriage return ('\r'). This is part of the newline character
            // and therefore an exception that should not be appended to the
            // string.
            string.append((char)readChar);

            // Read the next character
            readChar = reader.read();
        }
        return string.toString();
    }
    

我的问题是关于 readLine() 方法。在 while() 循环中，为什​​么我必须检查 readChar != -1 和 != '\n' ？据我了解，-1代表流的结束（EOF）。我的理解是，如果我提取一行，我只需要检查换行符。

谢谢。

Answer 1

请仔细阅读代码文档。你所有的疑问都在这里得到了很好的解答。

该函数正在检查“-1”，因为它正在处理那些没有换行符的流。在这种情况下，它将以字符串形式返回整个流。

Answer 2

这只是您（喜欢）将逻辑应用于您尝试做/实现的事情的方式。例如，上面的示例可以像他的那样编写，

private String readLine(InputStreamReader reader) throws IOException {
        // Test whether the end of file has been reached. If so, return null.
        int readChar = reader.read();
        if (readChar == -1) {
            return null;
        }else{
            StringBuffer string = new StringBuffer("");

            // Read until end of file or new line
            while (readChar != '\n') {
                // Append the read character to the string. Some operating systems
                // such as Microsoft Windows prepend newline character ('\n') with
                // carriage return ('\r'). This is part of the newline character
                // and therefore an exception that should not be appended to the
                // string.
                string.append((char)readChar);

                // Read the next character
                readChar = reader.read();
            }
            return string.toString();
        }
    }

所以之前的代码示例 readChar 检查 -1 只是安全检查。