how to check if an array doesn't contain a value using an if statement

Question

in my code i have created an array:

static BankClient clients[] = new BankClient[MAXCLIENTS]; // This array holds the clients up to a max of 1000

what i need to do is check this array to see if it contains a specific int. i was able to do this successfully through the use of a for loop and an if statement as shown below:

System.out.println("\n Ask for ID");
    System.out.println(">");
    IDInput = input.nextInt();              
    System.out.println("Check ID \n");

    for (int i = 0; i < clients.length; i++) 
    { 
        BankClient managementOptions = clients[i];
        
        if (managementOptions.getID() == IDInput) 
        {   
            // code in here                                 
        }

however, once i tried to put an else statement at the bottom to write an error message to the user, as a result of an invalid id, it proceed to print out an error for all ids saved in the array that do not match the id given by the user. this is what i wanted:

else if (// check if IDInput doesnt exist within the client array)
        {
            System.out.println("Error. Client does not exist.");
        }

however i cant seem to figure out what to put between the brackets. any help would be super appreciated! still pretty new to this website so if you need anymore information i will try my best to add it.

JP Moresmau · Accepted Answer · 2021-04-24 15:56:02Z

1

Simply keep track in the loop if you've found something:

boolean found=false;
for (int i = 0; i < clients.length; i++) 
    { 
        BankClient managementOptions = clients[i];
        
        if (managementOptions.getID() == IDInput) 
        {   
            found=true;                       
            break; // no need to search further
        } 
}
// no element found
if (!found){
 System.out.println("Error. Client does not exist.");
}

You cannot just print the error in the loop since you need to be sure you've looked at the whole array.

answered Apr 24, 2021 at 15:56

JP Moresmau

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5 Comments

mikasa7711 Over a year ago

this worked in terms of not printing out an error for every object in the array, but it still crashes when i enter something that doesn't exist in the array e.g the array has values 1,2,3,4 but i enter 7. how could i fix this? thanks for the help!

JP Moresmau Over a year ago

Define "crash". What happens? What exception and stack trace do you get?

mikasa7711 Over a year ago

this is the whole error that appears: Exception in thread "main" java.lang.NullPointerException: Cannot invoke "groupCoursework.BankClient.getID()" because "managementOptions" is null at groupCoursework.UserInterface.managementOptions(UserInterface.java:84) at groupCoursework.UserInterface.main(UserInterface.java:27) this appears when i enter something that doesnt exist in the array

JP Moresmau Over a year ago

Ah yes because some elements in the array are null. just have if (managementOptions!=null && managementOptios.getID() == IDInput) to only check the ID if the element is not null

JP Moresmau Over a year ago

And also if you can don't use Arrays. Use an ArrayList that can grow as needed and that would only contains non null values.

vincendep · Accepted Answer · 2021-04-24 16:01:26Z

0

System.out.println("\n Ask for ID");
System.out.println(">");
IDInput = input.nextInt();              
System.out.println("Check ID \n");

boolean isPresent = false;
for (int i = 0; i < clients.length; i++) { 
  BankClient managementOptions = clients[i];
     
  if (managementOptions.getID() == IDInput) {   
      
      isPresent = true 
      
      // code in here                                 
  }
}

if (! isPresent) {
  System.out.println("Error. Client does not exist.");
}

answered Apr 24, 2021 at 16:01

vincendep

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Comments

rhino_rus · Accepted Answer · 2021-04-24 17:37:38Z

0

Simple solution via Stream API:

Boolean isPresent = Arrays.stream(clients).anyMatch(x -> x.getID().equals(IDInput));

answered Apr 24, 2021 at 17:37

rhino_rus

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