Question

I’m running a java program I created that stores data inputted by user. Specifically 4 array lists which are songName, songArtist, songYear & songAlbum.
I have a user input for “songYear” and I only want the program to accept a maximum of 4 digits in length and give an error otherwise, how can this be achieved?

here’s the code I have for my add entry method:

        public void addEntry(){
        String newName = ui.getString("Enter the name of the track");
        songName.add(newName);
        String newArtist = ui.getString("Who performs this track");
        songArtist.add(newArtist);
        String newAlbum = ui.getString("What album is this track from");
        songAlbum.add(newAlbum);
        System.out.print("What year was the track released? ");
        int newYear=input.nextInt(4);
        songYear.add(newYear);

        System.out.println("\n" + "Thank you, " +songName.get(songName.size()-1) + " has been added to the library.");
        System.out.println("\n" + "Press 2 to view your library." + "\n");
    } 

Answer 1

You can use regex like: ^.{4}$

Means only if user typed 4 digits – return true, otherwise return false

To be sure that user used 4 numbers YYYY use something like:

^(?=[1-9]+)\d{4}$

Makes sure the year is 1 or 2 followed by three numbers; valid ranges in this case would be 1000-2999

^(?=[1-2][0-9]+)\d{4}$

Finally your code should be like:

 if(inputUserStr.matches("^(?=[1-2][0-9]+)\d{4}$")){
   // do some stuff
 }
  else{
   // print error about valid input form [YYYY]
  }