import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;

public class Solution {
  public void writeFile() {
      try {
          tryWriteFile();
      }catch(IOException e) {
          System.err.println("Hiba! A kiírás sikertelen!");
          System.err.println(e.getMessage());    
      }
  }

  public void tryWriteFile() throws IOException {
      try(
        FileOutputStream fos = new FileOutputStream("data.txt", true);
        OutputStreamWriter osw = new OutputStreamWriter(fos, "UTF-8")
      ) {
        osw.write("aaaa");
        osw.write(":bbbb");
        osw.write("\n");
      }      
  }
}