How to read several cases in java?

Reading until EOF? See how-to-detect-eof-in-java10.

Use a Scanner:

    Scanner scanner = new Scanner(System.in);
    while ( scanner.hasNext() ) {
    . . . 
    }

Or use a BufferedReader:

    BufferedReader r = new BufferedReader (new InputStreamReader (System.in));
    String s;
    while ( (s = r.readLine()) != null ) {
    . . .
    }

Generally, the BufferedReader is faster.