How to Append Data to Files Using Java FileWriter?

Appending to Files Using Java FileWriter with Append Mode

Writing to files in Java is a common task, especially for storing and retrieving data. The FileWriter class provides a convenient way to create new files or write to existing ones.

Appending to Existing Files

By default, FileWriter overwrites the contents of a file when writing to it. However, it's often desirable to append data to a file without erasing its existing contents. To achieve this, you can use the "append" mode.

Solution

To enable append mode, you need to pass true as the second argument to the FileWriter constructor:

FileWriter fout = new FileWriter(filename.txt", true);

This will open the file in append mode, causing any new writes to be added to the end of the file's current contents.

Example Usage

Consider the following code where FileWriter is used to write data to a file in append mode:

FileWriter fout = new FileWriter("filename.txt", true);
PrintWriter fileout = new PrintWriter(fout, true);
fileout.print(now.getTime().toString() + ", " + weight + ","+ count + "\n");
fileout.close();

In this example, the file "filename.txt" is opened in append mode using the FileWriter(... , true) constructor. The PrintWriter is then used to write data to the file. The true argument passed to the PrintWriter constructor ensures that the data is appended to the file rather than overwriting it.

By using FileWriter in append mode, you can easily add new data to existing files without losing any of the original contents. This makes it a useful technique for tasks such as logging and data accumulation.

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