I have a source code that is needed to be converted by creating classes, objects and methods. So far, I've just done by converting the initial main into a separate class. But I don't know what to do with constructor and which variables are supposed to be private. This is the code :

import java.util.*;

public class Card{

private static void shuffle(int[][] cards){

    List<Integer> randoms = new ArrayList<Integer>();
    Random randomizer = new Random();

    for(int i = 0; i < 8;) {
      int r = randomizer.nextInt(8)+1;
      if(!randoms.contains(r)) {
        randoms.add(r);
        i++;
      }
    }

    List<Integer> clonedList = new ArrayList<Integer>();
    clonedList.addAll(randoms);
    Collections.shuffle(clonedList);
    randoms.addAll(clonedList);
    Collections.shuffle(randoms);

    int i=0;

    for(int r=0; r < 4; r++){
        for(int c=0; c < 4; c++){
            cards[r][c] = randoms.get(i);
            i++;
        }
    }
}

public static void play() throws InterruptedException {

    int ans = 1;
    int preview;
    int r1,c1,r2,c2;
    int[][] cards = new int[4][4];
    boolean[][] cardstatus = new boolean[4][4];
    boolean gameover = false;
    int moves;
    Scanner input = new Scanner(System.in);

    do{
        moves = 0;

        shuffle(cards);

        System.out.print("Enter the time(0 to 5) in seconds for the preview of the answer : ");
        preview = input.nextInt();

        while((preview<0) || (preview>5)){
            System.out.print("Invalid time!! Re-enter time(0 - 5) : ");
            preview = input.nextInt();
        }

        preview = 1000*preview;
        System.out.println(" ");

        for (int i =0; i<4;i++){
            for (int j=0;j<4;j++){

                System.out.print(cards[i][j]);
                System.out.print(" ");
            }
            System.out.println("");
            System.out.println("");
        }

        Thread.sleep(preview);

        for(int b=0;b<25;b++){
            System.out.println(" ");
        }

        for(int r=0;r<4;r++){
            for(int c=0;c<4;c++){
                System.out.print("*");
                System.out.print(" ");
                cardstatus[r][c] = false;
            }
            System.out.println("");
            System.out.println(" ");
        }

        System.out.println("");

        do{
            do{
                System.out.print("Please insert the first card row : ");
                r1 = input.nextInt();
                while((r1<1) || (r1>4)){
                    System.out.print("Invalid coordinate!! Re-enter first card row : ");
                    r1 = input.nextInt();
                }

                System.out.print("Please insert the first card column : ");
                c1 = input.nextInt();
                while((c1<1) || (c1>4)){
                        System.out.print("Invalid coordinate!! Re-enter first card column : ");
                        c1 = input.nextInt();
                }

                if(cardstatus[r1-1][c1-1] == true){
                    System.out.println("The card is already flipped!! Select another card.");
                    System.out.println("");
                }
            }while(cardstatus[r1-1][c1-1] != false);

            do{
                System.out.print("Please insert the second card row : ");
                r2 = input.nextInt();
                while((r2<1) || (r2>4)){
                    System.out.print("Invalid coordinate!! Re-enter second card row : ");
                    r2 = input.nextInt();
                }

                System.out.print("Please insert the second card column : ");
                c2 = input.nextInt();
                while((c2<1) || (c2>4)){
                    System.out.print("Invalid coordinate!! Re-enter second card column : ");
                    c2 = input.nextInt();
                }

                if(cardstatus[r2-1][c2-1] == true){
                    System.out.println("The card is already flipped!! Select another card.");
                }
                if((r1==r2)&&(c1==c2)){
                    System.out.println("You can't select the same card twice!!");
                    continue;
                }
            }while(cardstatus[r2-1][c2-1] != false);

            r1--;
            c1--;
            r2--;
            c2--;

            System.out.println("");
            System.out.println("");
            System.out.println("");

            for(int r=0;r<4;r++){
                for(int c=0;c<4;c++){

                    if((r==r1)&&(c==c1)){
                        System.out.print(cards[r][c]);
                        System.out.print(" ");
                    }
                    else if((r==r2)&&(c==c2)){
                        System.out.print(cards[r][c]);
                        System.out.print(" ");
                    }
                    else if(cardstatus[r][c] == true){
                        System.out.print(cards[r][c]);
                        System.out.print(" ");
                    }
                    else{
                        System.out.print("*");
                        System.out.print(" ");
                    }
                }
                System.out.println(" ");
                System.out.println(" ");
            }

            System.out.println("");

            if(cards[r1][c1] == cards[r2][c2]){
                System.out.println("Cards Matched!!");

                cardstatus[r1][c1] = true;
                cardstatus[r2][c2] = true;
            }
            else{
                System.out.println("No cards match!!");
            }

            Thread.sleep(2000);

            for(int b=0;b<25;b++){
                System.out.println("");
            }

            for(int r=0;r<4;r++){
                for(int c=0;c<4;c++){
                    if(cardstatus[r][c] == true){
                        System.out.print(cards[r][c]);
                        System.out.print(" ");
                    }
                    else{
                        System.out.print("*");
                        System.out.print(" ");
                    }
                }
                System.out.println("");
                System.out.println(" ");
            }

            System.out.println("");
            System.out.println("");
            System.out.println("");

            gameover = true;

            for(int r=0;r<4;r++){
                for( int c=0;c<4;c++){
                    if(cardstatus[r][c]==false){
                        gameover = false;
                        break;
                    }
                }
                if(gameover==false){
                    break;
                }
            }

            moves++;

        }while(gameover != true);

        System.out.println("Congratulations, you won!!");
        System.out.println("It required " + moves + " moves to finish it.");
        System.out.println("");
        System.out.print("Would you like to play again? (1=Yes / 0=No) : ");
        ans = input.nextInt();

    }while(ans == 1);


}

}

The main class is:

import java.util.*;

public class PlayCard{

public static void main(String[] args) throws InterruptedException{

    Card game = new Card();
    game.play();

    }

}

Should I simplify the Card class by creating other classes?

Through this code, my javadoc has no constructtor. So i need help on this!