// Counter.java
// Solution to SA #5 by THC.  Based on the Counter class example.

// Implementation of the class Counter.

// Define a class of Counter objects. A Counter holds a single integer
// in the range 0..(myLimit - 1). Each time tick() is called the
// Counter increases, wrapping back to 0 when it reaches myLimit.

// Note: The show method always displays at least 2 digits, padding with
// a leading 0 if necessary. If the value of the Counter is >= 100, then
// the show method will display as many digits as necessary. That means
// that the columns of the successive Counter values displayed will not
// line up correctly when the Counter transitions from 99 to 100.

import java.text.DecimalFormat;

public class Counter {
  private int myLimit; // Upper limit on the counter
  private int myValue; // Current value

  // Constructor for the Counter class.
  // Create a Counter with myLimit set to limit and
  // myValue set to 0.
  public Counter(int limit) {
    myLimit = limit;
    myValue = 0;
  }

  // Display the value of a Counter, padding with a leading 0 if necessary.
  public void show() {
    DecimalFormat fmt = new DecimalFormat("00"); // Use at least 2 digits
    System.out.print(fmt.format(myValue));
  }

  // Increment the value of a Counter, wrapping around if it
  // hits the limit.
  public void tick() {
    myValue++;
    if (myValue == myLimit) // Has it hit the limit?
      myValue = 0; // Wrap if it has
  }
  
  // Advance the value of a Counter, wrapping around as appropriate.
  // The parameter gives how far to advance the value, and it may be negative.
  public void advance(int amount) {
    myValue = (myValue + amount) % myLimit;
    
    // If the counter ends up being negative, it will be between -1 and -myLimit.
    // Just add in myLimit to correct the value.
    if (myValue < 0)
      myValue = myLimit + myValue;
  }
}