how to get unique value from Arraylist java

Question

im using Contains method to evaluate customer1 set has cust object, but its keep on adding the same object(its not checking any duplicate)

 `List<Customer> customers = new ArrayList<Customer>();`
    `customers.add(new Customer(1, "A"));`
    `customers.add(new Customer(2, "B"));`
    `customers.add(new Customer(1, "B"));`
    `customers.add(new Customer(1, "C"));`
    `customers.add(new Customer(2, "A"));`
    `customers.add(new Customer(2, "B"));`
    `customers.add(new Customer(1, "A"));`
    `customers.add(new Customer(2, "C"));`
    `Set<Customer> customers1 = new HashSet<Customer>();`
    `for(Customer cust: customers) {`
        `if(!customers1.contains(cust)) {`
         `   customers1.add(cust);`
        `}`
    `}`

Expected Output:

[Customer{id=1, name='A'}, Customer{id=1, name='B'}, Customer{id=1, name='C'}, Customer{id=2, name='A'}, Customer{id=2, name='B'}]

See https://stackoverflow.com/questions/2265503/why-do-i-need-to-override-the-equals-and-hashcode-methods-in-java — PM 77-1, Mar 18 '21 at 22:31

score 0 · Answer 1 · answered Mar 18 '21 at 22:32

0

contains() internally calls equals() method to check for the identity so you have to overide equals() along with hashcode() method to check for Identity.

Below link will help you:

Why do I need to override the equals and hashCode methods in Java?

answered Mar 18 '21 at 22:32

Pradeep

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score 0 · Answer 2 · answered Mar 18 '21 at 22:33

0

First of all, you could just do

Set<Customer> customers1 = new HashSet<>(customers);

but your issue is mostlikely because your not overriding equals, hashcode

answered Mar 18 '21 at 22:33

Suic

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how to get unique value from Arraylist java

2 Answers2