可以通过在Activity的onCreate方法中重新启动模式为singleTop的Activity实例，从而保持当前Activity在栈顶，并避免被系统回收。代码示例如下：

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    private static final int REQUEST_CODE = 100;

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

        if (savedInstanceState == null) {
            Intent intent = new Intent(this, SingleTopActivity.class);
            intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
            startActivityForResult(intent, REQUEST_CODE);
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        Log.d(TAG, "onActivityResult: requestCode=" + requestCode + ", resultCode=" + resultCode);
    }
}

在上面的代码中，我们在MainActivity的onCreate方法中判断如果当前是第一次创建Activity，则启动SingleTopActivity，并将其设置为SingleTop启动模式，并通过startActivityForResult的方式等待其返回结果。SingleTopActivity可以为空Activity，只需要在其中重写onBackPressed方法让其立即结束即可，如下所示：

public class SingleTopActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        finish();
    }

    @Override
    public void onBackPressed() {
        finish();
    }
}