public class DoubleClickBackToContentTopListener implements View.OnClickListener { private final long delayTime = 300; private long lastClickTime = 0; private final IBackToContentTopView backToContentTopView; public interface IBackToContentTopView { void backToContentTop(); } @Override public final void onClick(View v) { long nowClickTime = System.currentTimeMillis(); if (nowClickTime - lastClickTime > delayTime) {  lastClickTime = nowClickTime; } else {  onDoubleClick(v); } } public DoubleClickBackToContentTopListener(@NonNull IBackToContentTopView backToContentTopView) { this.backToContentTopView = backToContentTopView; } public void onDoubleClick(View v) { backToContentTopView.backToContentTop(); }}

public class CNodeActivity extends Activity implements  DoubleClickBackToContentTopListener.IBackToContentTopView { private Toolbar toolbar; private ListView listView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_cnode); toolbar = (Toolbar) findViewById(R.id.toolbar); toolbar.setTitle(R.string.cnode); toolbar.setNavigationOnClickListener(v -> this.finish()); toolbar.setOnClickListener(new DoubleClickBackToContentTopListener(this)); listView = (ListView) findViewById(R.id.list_view);  listView.setAdapter(//TODO); initData(); } private void initData() { //TODO } @Override public void backToContentTop() { listView.setSelection(0); }}