JSON to POJO not working when same key is repeated in array

I have below json

{
    "startDate": "2021-02-01",
    "endDate": "2021-02-14",
    "columns": [
        {
            "attribute": "PID"
        },
        {
            "attribute": "CID"
        },
        {
            "attribute": "SID"
        }
    ],
    "ids": [
        {
            "id": "123456A",
            "idType": "PID"
        }
    ]
}

As you can see columns array have same key 'attribute'. I created pojo for this but i am not able to add data.

-----------POJO--------

public class Columns {

private String attribute;

public String getAttribute() {
    return attribute;
}

public void setAttribute(String attribute) {
    this.attribute = attribute;
}   
    
    
}

Other pojo

public List<Columns> getColumns() {
    return columns;
}
public void setColumns(List<Columns> columns) {
    this.columns = columns;
}

I am adding data like this

Columns c=new Columns();
        c.setAttribute("PID");
        List<Columns> l=new ArrayList<Columns>();
        l.add(c);
        c.setAttribute("CID");
        l.add(c);
        c.setAttribute("SID");
        l.add(c);
        m.setColumns(l);

and its giving output like this (value of m)

"columns": [
        {
            "attribute": "SID"
        },
        {
            "attribute": "SID"
        },
        {
            "attribute": "SID"
        }
    ],

What i am doing wrong ?

I think you should create a class Column (singular) so you can create a list like so:

List<Column> l=new ArrayList<Column>();
c = new Column();
c.setAttribute("PID");
l.add(c);
c2 = new Column();
c.setAttribute("SID");
l.add(c2);
...

You likely want to use a loop above.

In your current setup, you keep changing the c object which means that the last change you make to it will be assigned to all items (they all point to c).