This code writes the string to a file. It is important to close the writer, so this is done in a finally block.

 public void writeLineToFile(String str) throws IOException {
    File file = new File("file.txt");
    BufferedWriter bw = null;
    try {
      bw = new BufferedWriter(new FileWriter(file));
      bw.write(str);
    } finally {
      if (bw != null) {
        bw.close();
      }
    }
  }

Also note that write(String s) does not place newline character after string has been written. To put it use newLine() method.

Java 7 adds the java.nio.file (opens new window) package, and try-with-resources (opens new window):

public void writeLineToFile(String str) throws IOException {
    Path path = Paths.get("file.txt");
    try (BufferedWriter bw = Files.newBufferedWriter(path)) {
        bw.write(str);
    }
}

Syntax

• new BufferedWriter(Writer); //The default constructor
• BufferedWriter.write(int c); //Writes a single character
• BufferedWriter.write(String str); //Writes a string
• BufferedWriter.newLine(); //Writes a line separator
• BufferedWriter.close(); //Closes the BufferedWriter

Remarks

• If you try to write from a BufferedWriter (using BufferedWriter.write()) after closing the BufferedWriter (using BufferedWriter.close()), it will throw an IOException.
• The BufferedWriter(Writer) constructor does NOT throw an IOException. However, the FileWriter(File) constructor throws a FileNotFoundException, which extends IOException. So catching IOException will also catch FileNotFoundException, there is never a need for a second catch statement unless you plan on doing something different with the FileNotFoundException.