Java Programming Question: Intro to Computer Science

Question

I'm working on a project for my computer science class in java and it is a travel agency. In one of the classes, Basket, I need to make an array of objects of type Reservation. But I also have to have the following methods:

1. A constructor that takes no inputs and initialize the field with an array with no reservations.
2. A getProducts method which takes no inputs and returns a shallow copy of the array of Reservations of the basket. This array should contain all the reservations in the basket in the same order in which they were added.
3. An add method which takes as input a Reservation. The method adds the reservation at the end of the list of reservation of the basket and returns how many reservations are now there.
4. A remove method which takes as input a Reservation and returns a boolean. The method removes the first occurrence of the specified element from the array of reservation of the basket. If no such reservation exists, then the method returns false, otherwise, after removing it, the method returns true. Note that this method removes a reservation from the list if and only if such reservation is equal to the input received. For example, two flight reservations from Montreal to Vancouver are not considered equal if they were created under two different names. After the reservation has been removed from the array, the subsequent elements should be shifted down by one position, leaving no unutilized slots in the middle array. 

Here's what I have so far:

public Basket() {

ResList=null;

}

public Reservation [] getProducts() {

Reservation [] copy=ResList;

return copy;

}

public int add(Reservation r) {

int count=0;

Reservation newResList[] = new Reservation[ResList.length +1];

for(int i=0;i<ResList.length;i++) {

newResList[i]=ResList[i];

count++;

}

newResList[ResList.length]=r;

count++;

return count;

}

public boolean remove(Reservation r) {

int removeIndex=0;

Reservation newResList[] = new Reservation[ResList.length -1];

for(int i=0;i<ResList.length;i++) {

if(ResList[i].equals(r)) {

removeIndex=i;

}

}

for(int j = removeIndex; j < ResList.length -1; j++){

    newResList[j] = ResList[j + 1];

    return true;

   }

return false;

}

I tried to test these but I realized I can't call a method on an array. Like if I make an array of Reservations called rList and fill it with Reservations, I can't do rList.add(newReservation);

So I have 2 questions.

How can I actually use these methods to add or remove reservations in an array of reservations?

Does my code look somewhat correct?

Thank you so much I know it's a long question but any help is greatly appreciated because I've been stuck on this for several days now!

Answer 1

Did your instructor mention anything about using an ArrayList in your implementation of the Basket class? An ArrayList (https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html) is a class that represent a dynamic array. This means that you can add or remove elements from the ArrayList (by calling list.add(element), for example) without having to manually resize the array if you run out of space.

If you need any further help, I would love to get on a quick call to help you with the assignment!

Answer 2

Here is my advice and some real loose pseudo code:

(1) This past semester I had TWO students with EXACT same first AND last names. It got Real Ugly......

DO NOT compare reservations (or any record types for that matter) by names,locations, etc.

Use the RESERVATION #. Like an account # it is a UNIQUE primary key that DEFINITIVELY identities

the record.

(2) Write a Linear Search routine that identifies if a record with a specific reservation # is in the array

(3) Use TWO arrays.... one is a temporary that allows you to insert/delete records more easily....

Adding new record:

STEP 1: temp array is allocated with N+1.

STEP 2: Then copies current records into temp.

STEP 3: The new record is easily put at the end of the temp array.

STEP 4: Points the current array at temp increments the counter

VIOLA.... done

Deleting records requires TWO for loops....

STEP 1: call your Linear Search routine to verify the target record you want to kill is really in the array, storing the index of its location in the array; otherwise return a nasty negative value and bails out

Step 2: allocates temp with N-1 records.

Step 3: first for loop copies current records into the temp array STOPPING when you hit the target record

you want to kill;

Step 4: the second for loop skips OVER the target record you want to kill and copies the rest of the

current record

Step 5: points current array at temp, decrements the counter

(4) ALWAYS return deep copies of your data. Anyone who walks away with references and addresses to

you data can change it right under your nose , which incidentally undermines OOP principles.

With all of this said, I have uploaded WORKING code in the resources section under the TOOLKIT menu.

The filename is RESERVATION CODE.txt

It is a text file containing THREE (3) java source code classes (hence they must be compiled as three separate source code files)

1) Reservation.java : a simple reservation , which for now only contains the reservation #; that is after

all, only what you need anyway at this point

2) Reservations.java: manages and processes an ARRAY of reservations

3) ReservationBasket.java: main driver

Please take what I have said into serious consideration and THOROUGHLY peruse the code.

Let me know if there is anything you do not understand.

Thanks!