写好代码 [comments after India project]

这几天项目里事情不忙,我就向DY询问对我的一些comments,想不到由此引发了他给我开小灶讲解如何把代码写得更加优雅.

记下笔记:

1. Code could be written shorter, functionality is easy to implement, but we need to write it well.
2. Refactor had better not be in task list
3. software could be divided into 3 kinds: Life-Critical, Brand-Critical and Commercial.

Also he gave me and lily an exercise to write a small program cp, I think it's a good way to improve my programming.

Detailed comment from my code:

try catch in I/O operation
less comment, code is comment
linear code, such as:

convert

if (fileExists(src)){
     if(fileExists(des)&&!isCopyOverwrite(des)){
		return false;
	 }
     else if(fileExists(des)&&isCopyOverwrite(des)){
		return true;
     }
	 else{
		return true;
	 }
}
else{
}

to 

if (!fileExists(src)) {
     // src file does not exist
     printError(COPY_FAILURE_MSG);
     printError(src + " does not exist");
     return false;
}

if (!fileExists(des)) {
     return true;
}

if (isCopyOverwrite(des)) {
     printMessage("choose to overwrite the existing file " + des);
     return true;
}

接着他建议我去看一本<<敏捷软件开发>>的书.

最新消息说很有可能2个月后就换到一个做C++的产品里去,难道,两年不爽的Java生涯就此能够结束了吗?

练习的全部代码如下:

/**
 * 
 * <p>
 * try to write a java application to simulate ‘cp’ command, coping a source
 * file to a destination file.<br>
 * <br>
 * the basic is to read the source file byte by byte, then write to the
 * destination file.<br>
 * the command line is like:
 * 
 * <pre>
 * # java –cp . copy abc.txt dest.txt
 * </pre>
 * 
 * output proper error message to the user.<br>
 * 
 * @author xxx
 * 
 * 
 */
public class Copy {
	public static final String COPY_FAILURE_MSG = "failed to copy files";
	public static final String COPY_IO_ERROR_MSG = "failed to copy file because an I/O error occurs";
	public static final String COPY_USAGE = "Usage:\n\tjava [ -cp . ] Copy.jar source destination \n";

	public static void main(String[] args) {
		if (isInputValid(args)) {
			copyFile(args[0], args[1]);
		}
	}

	/**
	 * validate the input parameters<br>
	 * The parameter should be<br>
	 * 
	 * <pre>
	 * args[0] srouce file path
	 * args[1] destination file path
	 * </pre>
	 * 
	 * @param args
	 *            the input parameters in command line
	 * @return
	 * 
	 *         <code>false</code> paramters count is not 2 <br>
	 *         <code>true</code> if source file exists and destination file does
	 *         not exist<br>
	 *         <code>true</code> if source file exists and destination file
	 *         exist and user choose to overwrite it<br>
	 *         <code>false</code> if source file exists and destination file
	 *         exists and user choose not to overwrite it<br>
	 *         <code>false</code> if source file does not exist <br>
	 */
	private static boolean isInputValid(String[] args) {
		if (args.length != 2) {
			printError(COPY_FAILURE_MSG);
			printError(COPY_USAGE);
			return false;
		}

		String src = args[0];
		String des = args[1];
		if (!fileExists(src)) {
			printError(COPY_FAILURE_MSG);
			printError(src + " does not exist");
			return false;
		}

		if (!fileExists(des)) {
			return true;
		}

		if (isCopyOverwrite(des)) {
			printMessage("choose to overwrite the existing file " + des);
			return true;
		} else {
			printMessage("choose not to overwrite the existing file " + des);
			return false;
		}
	}

	/**
	 * check whether file <code>pathname</code> exist
	 * 
	 * @param pathname
	 * @return
	 */
	private static boolean fileExists(String pathname) {
		return new File(pathname).exists();
	}

	/**
	 * let use choose whether overwrite the existing file <code>des</code>
	 * 
	 * @param des
	 * @return
	 */
	private static boolean isCopyOverwrite(String des) {
		printMessage(des + " already exists, overwrite it? (y/n)");
		try {
			int input = System.in.read();
			if (input == 'y' || input == 'Y') {
				return true;
			} else {
				return false;
			}
		} catch (IOException e) {
			printMessage(COPY_IO_ERROR_MSG);
			return false;
		}
	}

	/**
	 * Copy the file <code>src</code> to <code>des</code> <br>
	 * print error message when failed to copy
	 * 
	 * @param src
	 *            source file path
	 * @param des
	 *            destination file path
	 */
	private static void copyFile(String src, String des) {
		try {
			printMessage("start to copy file");
			doRealCopyIO(src, des);
			printMessage("succeed to copy file");
		} catch (FileNotFoundException e) {
			printError(COPY_FAILURE_MSG);
			printError(src + " can't be read or " + des + " can't be written or " + des + " is directory");
		} catch (IOException e) {
			printError(COPY_FAILURE_MSG);
			printError(COPY_IO_ERROR_MSG);
		}
	}

	/**
	 * do the real copy file I/O
	 * 
	 * @param src
	 * @param des
	 * @throws IOException
	 */
	private static void doRealCopyIO(String src, String des) throws IOException {
		BufferedInputStream inputStream = null;
		BufferedOutputStream outputStream = null;
		try {
			inputStream = new BufferedInputStream(new FileInputStream(src));
			outputStream = new BufferedOutputStream(new FileOutputStream(des));
			int read;
			while ((read = inputStream.read()) != -1) {
				outputStream.write(read);
			}
			outputStream.flush();
		} catch (IOException e) {
			throw e;
		} finally {
			try {
				outputStream.close();
			} catch (Exception e2) {
			}
			try {
				inputStream.close();
			} catch (Exception e2) {
			}

		}

	}

	private static void printMessage(String string) {
		System.out.println(string);
	}

	private static void printError(String string) {
		System.err.println(string);
	}
}