I am continuing to study from the e-book “An introduction to Java Programming”. In that e-book, I use this method:
/**
* This method scans the array of cards in a for loop.
*/
public void getDetialsOfCards() {
// Declare a local variable.
MembershipCard card = null;
// note the use of the instanceof operator
for (int i = 0; i < noOfCards; i++) {
if (cards[i] instanceof DvdMembershipCard) {
card = cards[i];
System.out.println("This is a DVD card with " + getNoOnLoan()
+ " DVDs currently on loan.");
} else if (cards[i] instanceof GameMembershipCard) {
card = cards[i];
System.out.println("This is a games card with " +
getNoOnLoan() + " CDs currently on loan");
} else {
System.out.println("Neither type of card.");
}
} // End of for loop.
}
Here is my main method:
public class CompundIfElsegetDetialsOfCards {
// private static int noOfCards = 2;
private static int NoOnLoan;
private static Object[] cards;
private static DvdMembershipCard[] dvd = new DvdMembershipCard[6];
private static GameMembershipCard[] game = new GameMembershipCard[6];
private static MembershipCard card;
public static void getDetialsOfCards() {
// Declare a local variable.
int noOfCards = 6;
// note the use of the instanceof operator
for (int i = 0; i < noOfCards; i++) {
if (cards[i] instanceof DvdMembershipCard) {
card.equals(cards[i]);
System.out.println("This is a DVD card with " + getNoOnLoan()
+ " DVDs currently on loan.");
} else if (cards[i] instanceof GameMembershipCard) {
card.equals(cards[i]);
System.out.println("This is a games card with " +
getNoOnLoan() + " CDs currently on loan");
} else {
System.out.println("Neither type of card.");
}
} // End of for loop.
}
public static void main(String[] args) {
CompundIfElsegetDetialsOfCards.getDetialsOfCards();
}
private static int getNoOnLoan() {
System.out.println("jumlah Loan ");
return NoOnLoan;
}
private static class MembershipCard {
public MembershipCard() {
}
}
private int i;
private static class DvdMembershipCard {
public DvdMembershipCard() {
}
}
private static class GameMembershipCard {
public GameMembershipCard() {
}
}
}
The code compiles successfully but there is no output. What I must add to solve this?
Are you sure you are not receiving any exceptions.
You will receive
java.lang.NullPointerExceptionin the below lineYou have not assigned any object to
static Object[] cards;parameter you will receive the Null pointer exception.