1. Create a new class named BinaryNumbers and add the following method.

public static void countup(int n){
  if(n==0) {
    System.out.println("Blastoff!");
  } else {
    countup(n-1);
    System.out.println(n);
  }
}

2. Add a main method that calls the countUp method. Have the method take a number from the command-line.

public static void main(String[] args){
  int thenum = Integer.parseInt(args[0]);
  BinaryNumbers.countup(thenum);
}

The complete class should appear as follows.

public class BinaryNumbers {
  public static void countup(int n){
    if(n==0) {
      System.out.println("Blastoff!");
    } else {
      countup(n-1);
      System.out.println(n);
    }
  }
  public static void main(String[] args){
    int thenum = Integer.parseInt(args[0]);
    BinaryNumbers.countup(thenum);
  }
}

3. Compile the program and then run it with a parameter.

$ javac BinaryNumbers.java 
$ java BinaryNumbers 4 
Blastoff! 
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