In app Update (Flexible or Immediate)

 Dependency 

implementation 'com.google.android.play:core:1.9.0'

Java

AppUpdateManager appUpdateManager = AppUpdateManagerFactory.create(MainActivity.this);

        Task<AppUpdateInfo> appUpdateInfoTask = appUpdateManager.getAppUpdateInfo();

        appUpdateInfoTask.addOnSuccessListener(new OnSuccessListener<AppUpdateInfo>() {

            @Override

            public void onSuccess(AppUpdateInfo result) {

                if (result.updateAvailability() == UpdateAvailability.UPDATE_AVAILABLE

                        && result.isUpdateTypeAllowed(AppUpdateType.IMMEDIATE)) {  

      // FLEXIBLE for flexible

                    try {

                        appUpdateManager.startUpdateFlowForResult(result, AppUpdateType.IMMEDIATE, MainActivity.this, REQUEST_CODE);

                    } catch (IntentSender.SendIntentException e) {

                        e.printStackTrace();

                    }

                }

            }

        });

 @Override

    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {

        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == REQUEST_CODE){

            Toast.makeText(this, "Start Download", Toast.LENGTH_SHORT).show();

            if (requestCode != REQUEST_CODE){

                Log.d("hello","Update Flow Failed" + requestCode);

            }

        }

    }