如何判斷sim卡運營商

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.telephony.TelephonyManager;
import android.view.Menu;
import android.view.View;
import android.widget.Toast;

public  class MainActivity  extends Activity {

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

    @Override
     public  boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
         return  true;
    }
        
     public  void checkSIM(View v){
        TelephonyManager telManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE); 
        String operator = telManager.getSimOperator(); 
         if (operator !=  null){
             if (operator.equals("46000") || operator.equals("46002")){
                Toast.makeText( this, "此卡屬於(中國移動)", Toast.LENGTH_SHORT).show();
            }  else  if (operator.equals("46001")){
                Toast.makeText( this, "此卡屬於(中國聯通)", Toast.LENGTH_SHORT).show();                
            }  else  if (operator.equals("46003")){
                Toast.makeText( this, "此卡屬於(中國電信)", Toast.LENGTH_SHORT).show();                             }         }     }