I cannot get sum of the firebase data values in android studio

I am making an android app using android studio. I have linked it to firebase Realtime database. I want to retrieve the sum of some child values in one of the activities. This is my json file:-

{
  "Data" : {
    "UyhzVqsz1BVFKoePa2NEmlPFu382" : {
      "Budget" : {
        "Expanse" : {
          "Wedding" : {
            "stData1" : "W",
            "stData2" : "Wedding",
            "stData3" : "111",
            "stData4" : "11111"
          }
        }
      },
      "Traffic" : {
        "Wedding" : {
          "-MYKeSN8GZ8WbI-8TfVB" : {
            "stData1" : "15 Apr 2021,06:43:00:pm",
            "stData2" : "Wedding",
            "stData3" : "kkk",
            "stData4" : "100"
          },
          "-MYLu2qPmt9qj1tJPkrP" : {
            "stData1" : "16 Apr 2021,00:30:47:am",
            "stData2" : "Wedding",
            "stData3" : "ddd",
            "stData4" : "200"
          }
        }
      }
    }
  }
}

I have seen many possible solutions to this problem .I applied many of them in my app .But none of the worked. The following code worded a bit. Now the problem is that this code brings the value of the last entered data. I still cannot get the sum of all child nodes.

   myRef = myfire.getReference().child("Data").child(strUID).child("Traffic");

        myRef.child("Wedding").orderByChild("stData2").equalTo("Wedding").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for(DataSnapshot data: dataSnapshot.getChildren()) {
                    int sum = 0;
                    String value = data.child("stData4").getValue(String.class);
                    assert value != null;
                    int total = Integer.parseInt(value);

                    sum= sum + total;

                        tvBalance.setText(String.valueOf(sum));
                    }
                }


            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

Please give a practical example.

You're resetting the sum for each child node. To fix this pull the sum variable outside of the loop:

myRef = myfire.getReference().child("Data").child(strUID).child("Traffic");

myRef.child("Wedding").orderByChild("stData2").equalTo("Wedding").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        int sum = 0;
        for(DataSnapshot data: dataSnapshot.getChildren()) {
            String value = data.child("stData4").getValue(String.class);
            assert value != null;
            int total = Integer.parseInt(value);

            sum = sum + total;
        }
        tvBalance.setText(String.valueOf(sum));
    }


    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        throw databaseError.toException(); // never ignore errors
    }
});