******** I do not understand how using \"this \". in the code. Can someone expla

Question

********   I do not understand how using "this". in the code. Can someone explain to me how it works? Also, I need Method comments to be written for the code down below.****************

****** This is an example of what kind of Method comments I want. ********

/**

   Computes the volume of a cube.

   @param sideLength the side length of the cube

   @return the volume

*/

**********************

import java.util.*;

class Card
{
   private int rank;
   private char suit;

   public Card()
   {
       this.suit = 'S';
       this.rank = '1';
   }
   public Card(int r, char s)
   {
       this.suit = s;
       this.rank = r;
   }
   public void setCard(int r, char s)
   {
       this.rank = r;
       this.suit = s;
   }
   public int getRank()
   {
       return this.rank;
   }
   public char getSuit()
   {
       return this.suit;
   }
   public boolean equals(Card c)
   {
       return this.getRank() == c.getRank() && this.getSuit() == c.getSuit();
   }
   public int compareTo(Card c)
   {
       int ret = 0;
       if(this.getRank()-c.getRank()<0)ret = -1;
       if(this.getRank()-c.getRank()>0)ret = 1;
       return ret;
   }
   public String toString()
   {
       String r = "";
       switch(this.getRank())
       {
       case 1:r = "A";break;
       case 11:r = "J";break;
       case 12:r = "Q";break;
       case 13:r = "K";break;
       default:r = this.getRank()+"";
       }
       return r + this.getSuit();
   }
}

class Pile
{
   private ArrayList pile;
   public Pile()
   {
       pile = new ArrayList();
   }
   public Pile(int num)
   {
       pile = new ArrayList(num);
       if(num == 52)
       {
           char c = 'S';
           for(int j = 0; j<4; j++)
           {
               if(j == 1)c='H';
               if(j == 2)c='D';
               if(j == 3)c='C';
               for(int i = 1; i < 14; i++)
               {
                   this.pile.add(new Card(i,c));
               }
           }
       }

   }
   public Card dealCard()
   {
       Card c = pile.get(0);
       pile.remove(0);
       return c;
   }
   public boolean addCard(Card c)
   {
       return this.pile.add(c);
   }
   public boolean addPile(Pile p)
   {
       boolean ret = true;
       int i = 0;
       Pile p1 = new Pile(this.pile.size());
       while(ret)
       {
           if(!p1.pile.add(p.pile.get(i)))ret = false;
           i++;
       }
       if(ret)
       {
           i = 0;
           while(ret)
           {
               if(!this.pile.add(p.pile.get(i)))ret = false;
               i++;
           }
       }
       return ret;
   }
   public void shuffle()
   {
       for(int i= 0; i < 100; i++)
       {
           int r1 = (int)(Math.random()*this.pile.size());
           int r2 = (int)(Math.random()*this.pile.size());

           Card c1 = this.pile.get(r1);
           Card c2 = this.pile.get(r2);

           this.pile.set(r1, c2);
           this.pile.set(r2, c1);
       }
   }
   public String toString()
   {
       String ret = "";

       for(int i = 0; i < this.pile.size(); i++)
       {
           if(i % 10 == 0 && i != 0)ret+=" ";
           ret += this.pile.get(i)+" ";
       }
       return ret;
   }
}

public class Driver
{
   public static void main(String[] args)
   {
       Card c = new Card();
       c.setCard(3, 'A');

       System.out.println("Card1: " +c.toString());
       Card c2 = new Card(4, 'S');
       System.out.println("Card2: " + c2.toString());
       System.out.println("Card1 compared to Card2: " + c.compareTo(c2));
       System.out.println(c.equals(c2));

       Pile p = new Pile(52);
       System.out.println("Before shuffling: ");
       System.out.println(p.toString());

       p.shuffle();
       System.out.println("After shuffling: ");
       System.out.println(p.toString());
   }
}

Explanation / Answer

import java.util.*;

class Card
{
private int rank;
private char suit;
//this keyword is used to refer current class instance variable.
//eg: Card c = new Card() => this.suit is equivalent to c.suit. Since out constructor or function doesn't know c variable, we use this.
public Card() //public constructor to set with default values.
{
this.suit = 'S';
this.rank = '1';
}
public Card(int r, char s) //parameterized constructor.
{
this.suit = s;
this.rank = r;
}
public void setCard(int r, char s) //set the suit and rank
{
this.rank = r;
this.suit = s;
}
public int getRank() //return rank
{
return this.rank;
}
public char getSuit() //return suit
{
return this.suit;
}
//return true if two cards are equal.
// eg: a.equals(c); => a.rank is equivalent to this.rank. "this" basically refers to a
public boolean equals(Card c)
{
return this.getRank() == c.getRank() && this.getSuit() == c.getSuit();
}
//compare two cards. explanation of using "this" is same
public int compareTo(Card c)
{
int ret = 0;
if(this.getRank()-c.getRank()<0)ret = -1;
if(this.getRank()-c.getRank()>0)ret = 1;
return ret;
}
//prints the card.
public String toString()
{
String r = "";
switch(this.getRank())
{
case 1:r = "A";break;
case 11:r = "J";break;
case 12:r = "Q";break;
case 13:r = "K";break;
default:r = this.getRank()+"";
}
return r + this.getSuit();
}
}
//class of set of cards.
class Pile
{
private ArrayList pile;
public Pile()
{
pile = new ArrayList();
}
public Pile(int num)
{
pile = new ArrayList(num);
if(num == 52)
{
char c = 'S';
for(int j = 0; j<4; j++)
{
if(j == 1)c='H';
if(j == 2)c='D';
if(j == 3)c='C';
for(int i = 1; i < 14; i++)
{
this.pile.add(new Card(i,c));
}
}
}

}
public Card dealCard() //get the first card from pile
{
Card c = pile.get(0);
pile.remove(0);
return c;
}
public boolean addCard(Card c) //add the card to end of pile
{
return this.pile.add(c);
}
public boolean addPile(Pile p) //add pile of cards.
{
boolean ret = true;
int i = 0;
Pile p1 = new Pile(this.pile.size());
while(ret)
{
if(!p1.pile.add(p.pile.get(i)))ret = false;
i++;
}
if(ret)
{
i = 0;
while(ret)
{
if(!this.pile.add(p.pile.get(i)))ret = false;
i++;
}
}
return ret;
}
public void shuffle() //shuffle the cards position in pile
{
for(int i= 0; i < 100; i++)
{
int r1 = (int)(Math.random()*this.pile.size());
int r2 = (int)(Math.random()*this.pile.size());

Card c1 = this.pile.get(r1);
Card c2 = this.pile.get(r2);

this.pile.set(r1, c2);
this.pile.set(r2, c1);
}
}
public String toString() //prints the pile of cards
{
String ret = "";

for(int i = 0; i < this.pile.size(); i++)
{
if(i % 10 == 0 && i != 0)ret+=" ";
ret += this.pile.get(i)+" ";
}
return ret;
}
}
//class to test the program
public class Driver
{
public static void main(String[] args)
{
Card c = new Card();
c.setCard(3, 'A');

System.out.println("Card1: " +c.toString());
Card c2 = new Card(4, 'S');
System.out.println("Card2: " + c2.toString());
System.out.println("Card1 compared to Card2: " + c.compareTo(c2));
System.out.println(c.equals(c2));

Pile p = new Pile(52);
System.out.println("Before shuffling: ");
System.out.println(p.toString());

p.shuffle();
System.out.println("After shuffling: ");
System.out.println(p.toString());
}
}

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