Update element in the list while iterating Java8

Question

I have List of Customer object. I want to iterate over list and increment orders by one.

I tried with for each but here I had to create new list and add values in it.

class Customer{
    long id;
    int orders;
    //getters setters constructor
}

List<Customer> empList=Arrays.asList(new Customer(1,10),new Customer(2,,20));

List<Customer> empList1=new ArrayList<>();
empList.forEach(e->{
    e.orders++; //updating orders
    empList1.add(e);
});

Is there a better way to do this? I tried with streams but it is only mapping the orders

empList.stream().map(e->{e.orders++;}).collect(Collectors.toList());

You don’t need to create an another list emp1 as you are not modifying the structure of the list you are modifying the existing elements which is an object in this case. As you are using foreach which is a consumer in this case. Your fix should be e.setOrders(e.orders += 1). Then it will just update the existing list. — Vasanth Senthamarai Kannan
– Vasanth Senthamarai Kannan, Commented Apr 22, 2019 at 11:27
Possible duplicate of Modify property value of the objects in list using java 8 streams — Adrian
– Adrian, Commented Apr 22, 2019 at 12:11

Holger · Accepted Answer · 2019-04-24 10:33:50Z

3

You can use peek

empList.stream().peek(e->{e.orders++;}).collect(Collectors.toList());

Also as correctly pointed by "Vasanth Senthamarai Kannan " you don't need second list as you are not modifying structure of list,

empList.forEach(e->e.orders++);

edited Apr 24, 2019 at 10:33

Holger

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answered Apr 22, 2019 at 11:23

Vikas

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3 Comments

Holger Over a year ago

Or shorter: empList.forEach(e -> e.orders++);

Vikas Over a year ago

@Holger.. Yes.. Appreciate your feedback

Saqib Over a year ago

Peek method should only be used for debugging docs.oracle.com/javase/8/docs/api/java/util/stream/…

Hadi · Accepted Answer · 2019-04-22 11:31:05Z

0

you can use replaceAll() just define a method like incrementOrder()

empList.replaceAll(Customer::incrementOrder);


  public Customer incrementOrder(){
    this.orders+=1;
    return this;
  }

answered Apr 22, 2019 at 11:31

Hadi

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