In the following code, explain the meaning of case 49, case 50, and case 51.

boolean flag = false; //flag try { while (flag == false) { //- System.out.println("Please input a choice: "); int key = System.in.read(); switch (key) { case 49: System.out.println("User type: 1"); break; case 50: System.out.println("User type: 2"); break; case 51: System.out.println("User type: 3"); break;