How Do I Rename and Append to Files in Java?

Renaming a File in Java

Java provides a convenient way to rename files using the renameTo() method of the File class. This method takes another File object as an argument, representing the new name of the file.

Overwriting an Existing File

When renaming a file, if a file with the new name already exists, the renameTo() method will throw an IOException with the message "file exists". To handle this scenario, you can use the following code:

File file = new File("test.txt");
File file2 = new File("test1.txt");

if (file2.exists()) {
    throw new java.io.IOException("file exists");
}

boolean success = file.renameTo(file2);

If the renameTo() operation is successful, success will be set to true.

Appending to an Existing File

To append the contents of one file to an existing file, you can follow these steps:

1. Rename the first file to the existing file's name.
2. Create a new FileWriter with the append parameter set to true.
3. Write the contents of the first file to the FileWriter.

File file = new File("test.txt");
File file2 = new File("test1.txt");

file.renameTo(file2);

java.io.FileWriter out = new java.io.FileWriter(file2, true /*append=yes*/);
out.write("Hello world!");
out.close();

This code will rename the file test.txt to test1.txt and append the string "Hello world!" to the end of test1.txt.

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