Add items to List in Java

Question

I'm adding items to a List but the previous item always gets overwritten by later after the iteration.

List<CartPojo> cartLists = new ArrayList<CartPojo>();
CartPojo cartItem = new CartPojo();

for(int k=0; k<2; k++){
   cartItem.setItemName("name_"+k);
   cartLists.add(cartItem);
}

model.addAttribute("cartLists", cartLists);

This gives the output: name_1, name_1

Expected output: name_0, name_1

You're always adding the same object. Put CartPojo cartItem = new CartPojo(); into the for loop. — , Jun 11 '17 at 16:43
Create the new item inside the loop, not outside. Otherwise you're just adding the same item over and over. — Lew Bloch, Jun 11 '17 at 16:43
You can get more examples here: https://stackoverflow.com/questions/44486240/add-items-to-list-in-java and https://stackoverflow.com/questions/2697182/how-to-use-an-array-list — Vasyl Lyashkevych, Jun 11 '17 at 16:44

score 1 · Accepted Answer · answered Jun 11 '17 at 16:43

Currently, you're operating on the same instance throughout the iterations, rather you should instantiate the object inside the loop i.e:

for(int k=0; k<2; k++){
   CartPojo cartItem = new CartPojo();
   cartItem.setItemName("name_"+k);
   cartLists.add(cartItem);
}

score 0 · Answer 2 · answered Jun 11 '17 at 16:43

0

You are keep modifying the same object each time. You need to create Object inside the loop.

for(int k=0; k<2; k++){
   CartPojo cartItem = new CartPojo();
   cartItem.setItemName("name_"+k);
   cartLists.add(cartItem);
}

answered Jun 11 '17 at 16:43

Suresh Atta

120,458
37
198
307

score 0 · Answer 3 · answered Jun 11 '17 at 16:44

0

You are not declaring new "CartPojo" instances, so every time you do something on cartItem, it is the same object every time that is being manipulated.

answered Jun 11 '17 at 16:44

Meccano

537
4
8

score 0 · Answer 4 · answered Jun 11 '17 at 16:44

0

Just put Cartpojo cartItem=new CartPojo(); inside the for loop

List cartLists = new ArrayList();

for(int k=0; k<2; k++){

CartPojo cartItem = new CartPojo();

cartItem.setItemName("name_"+k);

cartLists.add(cartItem);

}

answered Jun 11 '17 at 16:44

Shaine

80
1
10

score 0 · Answer 5 · answered Jun 11 '17 at 16:44

You just need to create object every time inside the loop

List<CartPojo> cartLists = new ArrayList<CartPojo>();


for(int k=0; k<2; k++){
   CartPojo cartItem = new CartPojo();
   cartItem.setItemName("name_"+k);
   cartLists.add(cartItem);
}

model.addAttribute("cartLists", cartLists);

Peace

score 0 · Answer 6 · answered Jun 11 '17 at 16:45

You use the same object in all iterations. You should create an instance (with the new operator) at each time you want to create a CartPojo object.

Besides you should provide a constructor in CartPojo :

for(int k=0; k<2; k++){
    CartPojo cartItem = new CartPojo("name_"+k);
    cartLists.add(cartItem);
}

It makes the code more clear.

Add items to List in Java

6 Answers6