Can you help me solve this problem?

Write a toString method for the Deck class. It should return a single string that represents the cards in the deck. When it's printed, this string should display the same results as the print method in Section 13.1. Hint: You can use the + operator to concatenate strings, but it is not very efficient. Consider using java.lang.StringBuilder instead; see Section 10.11.

import java.util.Arrays; import java.util.Random;

/** * A deck of playing cards (of fixed length). */ public class Deck {

private Card[] cards;

/** * Constructs a standard deck of 52 cards. */ public Deck() { this.cards = new Card[52]; int index = 0; for (int suit = 0; suit <= 3; suit++) { for (int rank = 1; rank <= 13; rank++) { this.cards[index] = new Card(rank, suit); index++; } } }

/** * Constructs a deck of n cards (all null). */ public Deck(int n) { this.cards = new Card[n]; }

/** * Gets the internal cards array. */ public Card[] getCards() { return this.cards; }

/** * Displays each of the cards in the deck. */ public void print() { for (Card card : this.cards) { System.out.println(card); } }

/** * Returns a string representation of the deck. */ public String toString() { return Arrays.toString(this.cards); }

/** * Randomly permutes the array of cards. */ public void shuffle() { }

/** * Chooses a random number between low and high, including both. */ private static int randomInt(int low, int high) { return 0; }

/** * Swaps the cards at indexes i and j. */ private void swapCards(int i, int j) { }

/** * Sorts the cards (in place) using selection sort. */ public void selectionSort() { }

/** * Finds the index of the lowest card * between low and high inclusive. */ private int indexLowest(int low, int high) { return 0; }

/** * Returns a subset of the cards in the deck. */ public Deck subdeck(int low, int high) { Deck sub = new Deck(high - low + 1); for (int i = 0; i < sub.cards.length; i++) { sub.cards[i] = this.cards[low + i]; } return sub; }

/** * Combines two previously sorted subdecks. */ private static Deck merge(Deck d1, Deck d2) { return null; }

/** * Returns a sorted copy of the deck using selection sort. */ public Deck almostMergeSort() { return this; }

/** * Returns a sorted copy of the deck using merge sort. */ public Deck mergeSort() { return this; }

/** * Reorders the cards (in place) using insertion sort. */ public void insertionSort() { } }