CODEWITHSUNDEEP
javaarraysjson
suraj
suraj

Reputation: 61

How to create JsonArray using loop?

I am trying to create a JsonArray using a loop and adding the loop index to value, but getting last index in the JsonArray.

JSONArray array = new JSONArray();
JSONObject item = new JSONObject();
for(int i=0;i<2;i++) {
    item.put("information", "test"+i);
    item.put("id", 0+i);
    item.put("subName", "course"+i);
    //System.out.println(item.toString());
    array.add(item);
    System.out.println(array.toString());
}

Expected result:

[{"subName":"course0","information":"test0","id":0},
{"subName":"course1","information":"test1","id":1}]

Actual result:

[{"subName":"course1","information":"test1","id":1},{"subName":"course1","information":"test1","id":1}]

Upvotes: 1

Views: 137

Answers (1)

Michel K
Michel K

Reputation: 411

Your code only creates one JSONObject and then keeps modifying it. The following example illustrates this:

JSONArray array = new JSONArray();
JSONObject item = new JSONObject();
item.put("id", 0); 
array.add(item); 
// The next line overwrites the "id" in item. This also affects 
// the one already in the array because it's the same instance
item.put("id", 1); 
array.add(item); 
System.out.println(array.toString());

The array now contains the same instance twice. Result: [{"id":0}, {"id":0}]

JSONArray array = new JSONArray();
JSONObject item1 = new JSONObject();
item1.put("id", 0); 
array.add(item1); 
JSONObject item2 = new JSONObject();
item2.put("id", 1); 
array.add(item2); 
System.out.println(array.toString());

The array now contains two distinct instances. Result: [{"id":0}, {"id":1}]

In your code, you can solve the problem by moving the creation of the JSONObject instances into the loop:

for(int i=0;i<2;i++) {
    JSONObject item = new JSONObject(); // moved inside loop
    item.put("information", "test"+i);
    ...
    array.add(item); //

Upvotes: 1

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