Problem of the Day

Thursday, March 5, 2026

Problem:

The Bit class represents a binary digit that is either "on" or "off"—the boolean instance variable on is set to true then the bit is on, and false when the bit is off. A partial class description is given here.

public class Bit
{
    private boolean on;
    
    public Bit()
    {
        on = false;
    }

    /**
     * Changes the state of the switch
     * @return the new state of the switch.
     */
    public boolean flip()
    {
        /* missing code */
    }
}

The boolean method flip is intended to change the state of on to its opposite state, and return the new value of on. Which of the following could be used to replace /* missing code */ so that the method works correctly?

1. 
   

   if (on)
       on = false;
   else
       on = true;
   return on;

2. 
   

   if (on)
       return false;
   else
       return true;

3. 
   

   on = !on;
   return on;

1. I only
2. I and II only
3. II and III only
4. I and III only
5. I, II, and III

Show solution:

public boolean flip()
{
    return on = !on;
}