You are not telling the compiler that there is a chance to throw a FileNotFoundException a FileNotFoundException will be thrown if the file does not exist.
try this
public static void main(String[] args) throws FileNotFoundException {
File file = new File ("file.txt");
file.getParentFile().mkdirs();
try
{
PrintWriter printWriter = new PrintWriter(file);
printWriter.println ("hello");
printWriter.close();
}
catch (FileNotFoundException ex)
{
// insert code to run when exception occurs
}
}