SubstructTime.java

import java.time.LocalDateTime;
import java.util.Scanner;

public class SubstructTime {

  public static void main(String[] args) {
    LocalDateTime d = LocalDateTime.now();
    System.out.format("now: %tT", d);
    System.out.println();

    String[] term = { "hour", "minute", "second" };
    int[] sub = new int[term.length];
    Scanner in = new Scanner(System.in);
    for (int i = 0; i < term.length; ++i) {
      System.out.format("%s? ", term[i]);
      try {
        sub[i] = Integer.parseInt(in.next());
      } catch (Exception e) {
        e.printStackTrace(System.err);
      }
    }
    in.close();

    System.out.format(
        "sub: %tT",
        d.minusHours(sub[0]).minusMinutes(sub[1]).minusSeconds(sub[2])
    );
    System.out.println();
  }
}