在底部，我有一个通用的解决方案来替换文件中的行.但首先，这是手头特定问题的答案.辅助函数:

At the bottom, I have a general solution to replace lines in a file. But first, here is the answer to the specific question at hand. Helper function:

public static void replaceSelected(String replaceWith, String type) {
    try {
        // input the file content to the StringBuffer "input"
        BufferedReader file = new BufferedReader(new FileReader("notes.txt"));
        StringBuffer inputBuffer = new StringBuffer();
        String line;

        while ((line = file.readLine()) != null) {
            inputBuffer.append(line);
            inputBuffer.append('
');
        }
        file.close();
        String inputStr = inputBuffer.toString();

        System.out.println(inputStr); // display the original file for debugging

        // logic to replace lines in the string (could use regex here to be generic)
        if (type.equals("0")) {
            inputStr = inputStr.replace(replaceWith + "1", replaceWith + "0"); 
        } else if (type.equals("1")) {
            inputStr = inputStr.replace(replaceWith + "0", replaceWith + "1");
        }

        // display the new file for debugging
        System.out.println("----------------------------------
" + inputStr);

        // write the new string with the replaced line OVER the same file
        FileOutputStream fileOut = new FileOutputStream("notes.txt");
        fileOut.write(inputStr.getBytes());
        fileOut.close();

    } catch (Exception e) {
        System.out.println("Problem reading file.");
    }
}

然后调用它:

public static void main(String[] args) {
    replaceSelected("Do the dishes", "1");   
}

原始文本文件内容:

---

Original Text File Content:

洗碗0
喂狗0
打扫了我的房间1

Do the dishes0
Feed the dog0
Cleaned my room1

输出:

洗碗0
喂狗0
打扫了我的房间1
----------------------------------
洗碗1
喂狗0
打扫了我的房间1

Do the dishes0
Feed the dog0
Cleaned my room1
----------------------------------
Do the dishes1
Feed the dog0
Cleaned my room1

新的文本文件内容:

洗碗1
喂狗0
打扫了我的房间1

Do the dishes1
Feed the dog0
Cleaned my room1

注意，如果文本文件是:

---

And as a note, if the text file was:

洗碗1
喂狗0
打扫了我的房间1

Do the dishes1
Feed the dog0
Cleaned my room1

并且您使用了方法 replaceSelected("Do the盘", "1");,它不会改变文件.

and you used the method replaceSelected("Do the dishes", "1");, it would just not change the file.

由于这个问题非常具体，我会在这里为未来的读者添加一个更通用的解决方案(基于标题).

Since this question is pretty specific, I'll add a more general solution here for future readers (based on the title).

// read file one line at a time
// replace line as you read the file and store updated lines in StringBuffer
// overwrite the file with the new lines
public static void replaceLines() {
    try {
        // input the (modified) file content to the StringBuffer "input"
        BufferedReader file = new BufferedReader(new FileReader("notes.txt"));
        StringBuffer inputBuffer = new StringBuffer();
        String line;

        while ((line = file.readLine()) != null) {
            line = ... // replace the line here
            inputBuffer.append(line);
            inputBuffer.append('
');
        }
        file.close();

        // write the new string with the replaced line OVER the same file
        FileOutputStream fileOut = new FileOutputStream("notes.txt");
        fileOut.write(inputBuffer.toString().getBytes());
        fileOut.close();

    } catch (Exception e) {
        System.out.println("Problem reading file.");
    }
}