public class MainActivity extends AppCompatActivity {

    ExpandableListAdapter listAdapter;
    ExpandableListView expListView;
    List<String> listDataHeader;
    HashMap<String, List<String>> listDataChild;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // get the listview
        expListView = findViewById(R.id.lvExp);

        // preparing list data
        prepareListData();
        listAdapter = new ExpandableListAdapter(this, listDataHeader, listDataChild);

        // setting list adapter
        expListView.setAdapter(listAdapter);

        //  PEGA A POSIÇÃO DO ITEM DA LISTA
        expListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {
            @Override
            public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {
                Log.i("LOG", "Posição: " + childPosition);

                parent.collapseGroup(0);

                return false;
            }
        });

        //  TROCA O ICONE DE EXPANSAO
        expListView.setGroupIndicator(getResources().getDrawable(R.drawable.ic_launcher_background));
    }

    private void prepareListData() {
        listDataHeader = new ArrayList<>();
        listDataChild = new HashMap<>();

        // Adding child data
        listDataHeader.add("Lista de itens");

        // Adding child data
        List<String> itens = new ArrayList<String>();
        itens.add("Item 1");
        itens.add("Item 2");
        itens.add("Item 3");
        itens.add("Item 4");
        itens.add("Item 5");

        listDataChild.put(listDataHeader.get(0), itens); // Header, Child data

    }
}

public class ExpandableListAdapter extends BaseExpandableListAdapter {
    String headerTitle;
    private Context ctx;
    private List<String> listDataHeader; // header titles
    // child data in format of header title, child title
    private HashMap<String, List<String>> listDataChild;

    public ExpandableListAdapter(Context ctx, List<String> listDataHeader, HashMap<String, List<String>> listChildData) {
        this.ctx = ctx;
        this.listDataHeader = listDataHeader;
        this.listDataChild = listChildData;
    }

    @Override
    public Object getChild(int groupPosition, int childPosititon) {
        return this.listDataChild.get(this.listDataHeader.get(groupPosition)).get(childPosititon);
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    @Override
    public View getChildView(int groupPosition, final int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {

        final String childText = (String) getChild(groupPosition, childPosition);

        if (convertView == null) {
            LayoutInflater infalInflater = (LayoutInflater) this.ctx.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(R.layout.item_lista, null);
        }

        TextView tvItemLista = convertView.findViewById(R.id.tvw_item_nome);
        tvItemLista.setText(childText);

        return convertView;
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return this.listDataChild.get(this.listDataHeader.get(groupPosition))
                .size();
    }

    @Override
    public Object getGroup(int groupPosition) {
        return this.listDataHeader.get(groupPosition);
    }

    @Override
    public int getGroupCount() {
        return this.listDataHeader.size();
    }

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        headerTitle = (String) getGroup(groupPosition);
        if (convertView == null) {
            LayoutInflater infalInflater = (LayoutInflater) this.ctx.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(R.layout.list_group, null);
        }

        TextView tvTitleHeader = convertView.findViewById(R.id.tvw_title_header);
        tvTitleHeader.setTypeface(null, Typeface.BOLD);
        tvTitleHeader.setText(headerTitle);

        return convertView;
    }

    public void changeHeader(String text){
        headerTitle = text;
    }

    @Override
    public boolean hasStableIds() {
        return false;
    }

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}