Java create Customer function gives random values

I'm working on a insert customers in system project. It is working in tomcat, and is a maven project. Since I started a new project; some things work; some things don't. I made a createCustomer function:

public static Customer createCustomer(String name){
    if (allCustomers.stream().noneMatch(e->e.getName().equals(name))) {
        Customer newCustomer = new Customer(name);
        allCustomers.add(newCustomer);
        return newCustomer;
    }
    else return null;
}

When I run my BootupListener; I entered:

    Customer.createCustomer("Maikol");
    Customer.createCustomer("Henk");
    nl.hu.bep.model.Customer.createCustomer("Sjon");

    System.out.println(Customer.getAllCustomers());
    System.out.println(Customer.getCustomer(1));
    System.out.println(Customer.getCustomerById(1));

Which strangely gives the prints:

[nl.hu.bep.model.Customer@94bfdfef, nl.hu.bep.model.Customer@4263369, nl.hu.bep.model.Customer@4c37fee]
nl.hu.bep.model.Customer@94bfdfef
nl.hu.bep.model.Customer@94bfdfef

nl.hu.bep is my package tag, and Customer is the class where createcustomer is located.
Why does it not work?

I don't think it gives different outputs.

All customers with the object specifiers are, respectively, -> 94bfdfef, 4263369, 4c37fee

As far as we know, the last 2 outputs show conspicuously that both are involved in the Customers maintained.

The issue(if it is a issue), imho, stems from the data structure hold the users. There is no order for Set data structure, for instance. If you map(using HashMap) the ids with the customer numbers, there is still no oder guarantee at all that of data structure.

When you print a collection, it prints [, then a comma separated list of all the items inside, and then ]. And to print 'an item', it invokes that item's toString() method (unless it is null, then it prints null).

The toString() in java.lang.Object has absolutely no idea what to do, so it just prints the name of the type, followed by an @, followed by the system identity hashcode, which is meaningless, and will change on every JVM invocation.

The solution is to implement toString methods. Your Customer method SHOULD be:

public class Customer {
    private String name;
    // other fields here

    @Override public String toString() {
        return "Customer: " + name;
    }
}