Check if an object already exists in Java ArrayList

Question

I want to check whether a patient object already exists in an ArrayList queue using the unique ID nhsNumber. But when I add a patient to the queue who I know already exists in the queue, the following code does not detect it. Any idea why this is?

public boolean checkIfInQueue(Patient p) {
    // set nhsNumber equal to the nhsNumberLabel on the page
    String nhsNumber = nhsNumberLabel.getText();
    System.out.println("Checking if " + nhsNumber + " already in the queue");

    // create boolean to state whether a person is in the queue or not (defaults to false)
    boolean isInQueue = false;

    for (int i = 0; i < Queue.queue.size(); i++) {
      if (Queue.queue.size() == 0) {
        System.out.println("Queue is empty");
        isInQueue = false;
        break;
      } else if (Queue.queue.get(i).getNhsNumber() == p.getNhsNumber()) {
        System.out.println(p.getFirstName() + " is already in the queue (checkIfInQueue() method)");
        isInQueue = true;
        break;
      } else {
        System.out.println(p.getFirstName() + " is not is the queue (checkIfInQueue() method)");
        isInQueue = false;
      }
    }

    return isInQueue;
  }

thanks, K

I think u should use: Queue.queue.get(i).getNhsNumber().equals(p.getNhsNumber()) — MarsPeople, Apr 26 '15 at 16:09

score 3 · Answer 1 · answered Apr 26 '15 at 16:06

You can do this in a more standard and elegant way.

Override the equals() method in the Patient class.

public boolean equals(Object obj){
    if(obj instanceof Patient){
        return ((ThisClass)obj.getNhsNumber().equals(this.getNhsNumber());
    }
    return false;
}

Then call queue.contains() to check if the queue contains the object.

Queue.queue.contains(p) // Call the contains method with the p object.

contains() will loop through the queue and check if the objects are equal to your p object by calling .equals().

thanks Sam, I will try this method. My original error was using `==` instead of `.equals()` — KvnH, Apr 26 '15 at 16:11

score 0 · Answer 2 · answered Apr 26 '15 at 16:04

0

For every elements which is not a primitive, you need to use equals() instead of ==.

Moreover you should read the Javadoc of Set. This collection avoid you to check if you already store the Patient and the performances will be really better.

answered Apr 26 '15 at 16:04

Happy

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score 0 · Answer 3 · answered Apr 26 '15 at 16:10

    if (Queue.queue.size() == 0) {
        System.out.println("Queue is empty");
        isInQueue = false;
        break;
      } 
      >> This code does not serve purpose because the for loop already check the condition of 0.

    Modify like this
    for (int i = 0; i < Queue.queue.size(); i++) {
       String nhsnumber=Queue.queue.get(i).getNhsNumber();
       if (nhsnumber.equalIgnoreCase(p.getNhsNumber())==true) {
        System.out.println(p.getFirstName() + " is already in the queue (checkIfInQueue() method)");
        isInQueue = true;
        break;
      } else {
        System.out.println(p.getFirstName() + " is not is the queue (checkIfInQueue() method)");
        isInQueue = false;
      }
      }

     >> isInQueue variable is also not used so remove the variable if its not used

**isInQueue** It isn't used in this snippet, but it probably is later on in the code. — SamTebbs33, Apr 26 '15 at 16:52

Check if an object already exists in Java ArrayList

3 Answers3