Creating a method that returns a random number and moves items in array

I recently posted to question about my toString method that thankfully was answered by someone on the forum. Now I am having some trouble with getting the results I want from my getRandomCard() method. I will post the entire page of code but this is what I am trying to achieve:

-get a random number (lets say it it 52) -now create a temp card to return so I can make the value null. - I want to now amend my array so that the card I just used is replaced by the last number in the deck that has a value - which is why I have the variable cardsRunning.

If anyone can see where I am going wrong I would love some help.

public class Deck {

private Card[] card = new Card[100];
private int cardsRunning = 100;
static int DECKSIZE = 100;
static java.lang.String emailID = "MITNY013";
private boolean random = true;

/**
 * Constructor for the Deck. Adds the following cards to the deck in the following order
 * 4x Super Lucky Strike, Damage 100, Mana 2 
 * 6x Mega Santa Hit, Damage 80, Mana 2
 * 10x Critical Hit, Damage 50, Mana 5
 * 10x Massive Strike, Damage 40, Mana 7
 * 15x Wrong Way Down A One Way Street, Damage 30, Mana 10
 * 15x Bender Rules Here, Damage 15, Mana 10
 * 40x Trade, Damage 5, Mana 5 <br>
 * My solution length: 16 lines (space lines not included)
 * @param random - Whether to turn on random features
 */

public Deck(boolean random) {
    for (int index = 0; index <= 3; index++) {
        card[index] = new Card( 2, 100, "Lucky Strike");
    }
    for (int index = 4; index <= 10; index++) {
        card[index] = new Card( 2, 80, "Santa Hit");
    }
    for (int index = 11; index <= 20; index++) {
        card[index] = new Card( 5, 50, "Critical Hit");
    }
    for (int index = 21; index <= 30; index++) {
        card[index] = new Card ( 7, 40, "Massive Strike");
    }
    for (int index = 31; index <= 45; index++) {
        card[index] = new Card( 10, 30, "Wrong Way Down A One Way Street");
    }
    for (int index = 46; index <= 60; index++) {
        card[index] = new Card( 10, 15, "Bender Rules Here");
    } 
    for (int index = 61; index <= 99; index++) {
        card[index] = new Card( 5, 5, "Trade");
    } 
}

/**
 * Returns a string representation of the entire deck in the format
 * Deck [ 1:Card [name=Super Lucky Strike, manaCost=2, damageDone=100]
 *        2:Card [name=Super Lucky Strike, manaCost=2, damageDone=100]
 *        3:Card [name=Super Lucky Strike, manaCost=2, damageDone=100]
 *        4:Card [name=Super Lucky Strike, manaCost=2, damageDone=100]] <br>
 * My solution length: 5 lines
 * @overrides - toString in class java.lang.Object
 */

@Override
public String toString() {
    StringBuilder sb = new StringBuilder();
    for (int index = 0; index < card.length; index++) {
        sb.append((index + 1) + ": " +  card[index].toString() + "\n");
    }
    return sb.toString();
}

/**
 * Uses a random number generator to get a card from the deck somewhere then swaps the 
 * last card in the deck to that position and reduces the cardsRemaining by one. 
 * This is important. if the random flag is false you should always get the card at 
 * position 0. When you swap the card out you should also set the old position to null 
 * for safety. <br>
 * My solution length: 10 lines
 * @return - the card drawn or null if no cards left in deck
 */

public Card getRandomCard() {
    // use random number generator
    Random rand = new Random();
    int randomCardNo = rand.nextInt(this.cardsRunning);
    Card newCard = this.card[randomCardNo];
    //reorder the array - swaps the last card in the deck to that position
    card[randomCardNo] = card[getCardsRemaining() -1];
    card[getCardsRemaining() -1] = null;
    this.cardsRunning--;
    if (this.cardsRunning == 0) {
        return null;
    }
    else {
        return newCard;}
}

/**
 * Return the number of cards remaining in the deck.
 * My solution length: 1 lines
 * @return - the total cards remaining
 */

public int getCardsRemaining() {
    return this.cardsRunning;}}