Why my Model class, data is incorrect?

Question

Why my Model class data is incorrect?

enter image description here

List<DataMasterList> dataMasterLists = new ArrayList<DataMasterList>();

private void addMaster() {
    for (int i = 0; i < 6; i++) {
        DataMasterList dataMasterList = new DataMasterList();
        dataMasterList.setMaster_code("000" + i);
        dataMasterList.setProduct_name("name" + i);
        dataMasterList.setAmount(4 + i + "");
        dataMasterList.setUnit_price(10 + "");
        dataMasterLists.add(dataMasterList);
        Log.d("test1",dataMasterLists.get(i).getMaster_code()+" ");
    }

    Log.d("test2",dataMasterLists.get(0).getMaster_code()+" ");
}

Content of Log.d:

test1: 0000
test1: 0001
test1: 0002
test1: 0003
test1: 0004
test1: 0005

test2: 0005

Why does test2 = 0005 ?

Why every value in dataMasterLists is 0005 ?

According to this https://stackoverflow.com/a/19843507/4730957, it could be due to static fields in the class. Can you please add the DataMasterList class code? — Gopalakrishna Kini, Oct 17 '17 at 09:22
@Gopalakrishna Kini found a good example , as i see your confusion about this , i answer to the question to make you understand the principal difference between what you expect and what you got — Frank, Oct 17 '17 at 09:58
Looking at the image, you can see that IntelliJ shows the methods in *cursive*. Which is an indicator that those methods are `static`. Static fields are "global" to the class. So if your instances rely on those fields, they're all going to have the same values. — QBrute, Oct 17 '17 at 10:37

score 0 · Accepted Answer · answered Oct 17 '17 at 09:52

The problem is about access modifiers which change the fields class behaviour . You are making confusion with class instance variable and class variable .

Case 1 (instance variable )

public class DataMasterList {

    private String masterCode;

    public DataMasterList() {
        // TODO Auto-generated constructor stub
    }

    public  String getMasterCode() {
        return this.masterCode;
    }

    public  void setMasterCode(String masterCode) {
        this.masterCode = masterCode;
    }

private String masterCode; you can access to this field only with accessor methods and when you create a new instance , each instance will have own field.

case 2 (static variable )

public class DataMasterList {

    static String masterCode;

    public DataMasterList() {
        // TODO Auto-generated constructor stub
    }

    public static String getMasterCode() {
        return masterCode;
    }

    public static void setMasterCode(String masterCode) {
        DataMasterList.masterCode = masterCode;
    }

}

static String masterCode; you can access to the field directly without accessor methods and without create any instance of the object . Anyway if you create instances like in your case , when you modify the last time the masterCode it willl effect all instances.

Why my Model class, data is incorrect?

1 Answers1