/**
 * 
 * This class provides the behaviour of a Pair (2-tuple) of data values<br>
 * The 2 data are chosen from a simple enumeration of 3 values - EL1, EL2, EL3 <br>
 * These values  <u>must never be the same</u>
 * @author J Paul Gibson
 * @version 1
 */
public class PairOfData {

	/**
	 * The Data values for the Pair elements
	 * @author gibson
	 *
	 */
	enum Data {EL1, EL2, EL3};
	
	/**
	 * The first element of the Pair of Data
	 */
	private Data first;
	
	/**
	 * The second element of the Pair of Data
	 */
	private Data second;
	
    /**
     * 
     * @param d1 First data element
     * @param d2 Second data element
     */
	PairOfData (Data d1, Data d2){
		if (d1!= d2) {first = d1; second = d2;}
	}
	
	/**
	 * 
	 * @return First data element
	 */
	public Data get_first(){return first;}
	
	/**
	 * 
	 * @param new_first New value for First data element
	 */
	public void set_first (Data new_first){first = new_first;}
	
	/**
	 * 
	 * @return Second data element
	 */
	public Data get_second(){return second;}
	
	/**
	 * 
	 * @param new_first New value for First data element
	 */
	public void set_second (Data new_first){second = new_first;}
	
	/**
	 *  Generate string representation as (<em>first</em>, <em>second</em>)
	 */
	public String toString(){ return "("+ first+", "+second+")";}
	
	/**
	 * Simple self-test - for students - with results output to screen
	 * @param args expected to be empty
	 */
	public static void main (String args []){
		PairOfData p = new PairOfData(Data.EL1, Data.EL1);
		System.out.println("Created the pair "+ p);
	}
	
}// ENDCLASS PairOfData