/**
 * DNA class represents the DNA strand. 
 * 
 * @author  ... (your name goes here)
 * @version ... (date goes here)
 */ 
public class DNA 
{
    //DNA sequence of nucleotide basis
    private String sequence; 
    //valid/invalid indicator 
    private boolean valid; 

    /**
    * Initializes newly created DNA strand to the provided
    * sequence. The sequence is validated to contain only
    * legal nucleotides: guanine (G), adenine (A),
    * thymine (T), or cytosine (C). 
    * @param sequence the sequence of nucleotide basis to be used
    *    in this DNA 
    */
    public DNA ( String sequence ) {

    }

    /*
    * Operates on the sequence of this DNA object. It returns true/false 
    * indicating validity of the sequence. The sequence is valid if it contains
    * only legal nucleotide basis: guanine (G), adenine (A),
    * thymine (T), or cytosine (C). The valid data field is set accordingly. 
    * @return true if the sequence in this DNA object is valid, false otherwise
    */
    private boolean  validate () { 

    }

    /** 
    * Translates this DNA object to its corresponding RNA sequence. The DNA and RNA
    * are closely related. The major difference is that the RNA contains
    * uracil (U) rather than thymine (T). This method replaces every occurrence of T
    * in the sequence by U and returns the corresponding String object. 
    * @return the RNA sequence 
    */
    public String toRNA () {

    }

    /**
    * Computes the complementary DNA strand. The DNA usually exists as a double 
    * helix: given the strand stored in this DNA object, this method computes
    * and returns the second strand from the helix. To compute the complementary 
    * strand all A's need to be swapped with T's (and vice versa) and all C's need 
    * to be swapped with G's (and vice versa), and then the rerulting string is 
    * reversed.
    * @return DNA object containing the reverse complement of the sequence stored
    *    in this DNA object 
    */
    public DNA reverseComplement () {

    }

    /**
    * Returns true if this DNA object contains a valid strand and false otherwise.
    * @return true if this DNA object contains a valid strand and false otherwise
    */
    public boolean isValid () {

    }

    /**
    * Returns the String representation of this DNA object which is the sequence 
    * itself.
    */
    public String toString () {

    }
}