OptionsjMenu.java

@Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.register, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_cancel:
                finish();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }
    
    <?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
    >
    <item
        android:id="@+id/action_cancel"
        android:orderInCategory="100"
        android:title="Cancel"
        android:icon="@drawable/ic_clear_white_24dp"
        app:showAsAction="always"
        />
</menu>