@OptionsItem(android.R.id.home)
    void homeClicked() {
        finish();
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int itemId_ = item.getItemId();
        if (itemId_ == android.R.id.home) {
            homeClicked();
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    import android.R;

    ...

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int itemId_ = item.getItemId();
        if (itemId_ == R.id.home) {
            homeClicked();
            return true;
        }
        return super.onOptionsItemSelected(item);
    }