为什么在使用对话框时显示此错误：MainActivity类型的OnCreate（Bundle）方法必须覆盖或实现超类型方法

Question

我有一个问题： - 当我在代码中使用对话框或吐司时，显示以下错误：方法OnCreate（Bundle）类型MainActivity必须覆盖或实现超类型方法。

所以我测试了jdk编译器1.5,1.6和1.7的3状态，但它不起作用。 有什么问题？

public class MainActivity extends Activity {

boolean stopCopy = false;
boolean stopDelete = false;
boolean isCopy = false;
boolean isDelete = false;

private ProgressBar pr;

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

    final EditText edittxt_start_copy = (EditText) findViewById(R.id.edittxt_start_num);
    final EditText edittxt_end_copy = (EditText) findViewById(R.id.edittxt_end_num);
    final Button btn_start_copy = (Button) findViewById(R.id.btn_start_copy);


    pr = (ProgressBar) findViewById(R.id.progressBar);
    pr.setVisibility(View.GONE);

    final EditText edittext_start_delete = (EditText) findViewById(R.id.edittxt_start_delete);
    final EditText edittext_end_delete = (EditText) findViewById(R.id.edittxt_end_delete);
    final Button btn_start_delete = (Button) findViewById(R.id.btn_start_delete);

    btn_start_copy.setOnClickListener(new OnClickListener() 
    {

        @Override
        public void onClick(View v)
        {
            if(!isCopy)
            {
                btn_start_copy.setText("STOP");
                pr.setVisibility(View.VISIBLE);

            stopCopy = false;

            // Check if no view has focus:
            View view = MainActivity.this.getCurrentFocus();
            if (view != null)
            {  
                InputMethodManager imm = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
                imm.hideSoftInputFromWindow(view.getWindowToken(), 0);
            }


            final String start_str_copy = edittxt_start_copy.getText().toString();
            String end_str_copy = edittxt_end_copy.getText().toString();

            final String start_num_copy = start_str_copy.substring(4,11);
            final String end_num_copy = end_str_copy.substring(4,11);

            if (start_str_copy.length() < 11 || end_str_copy.length() < 11)
            {
                AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                builder.setTitle("خطا").setMessage("شماره وارد شده باید یازده رقمی باشد");
                AlertDialog alert = builder.create();
                alert.show();

            }
            else
            {

            Thread copy = new Thread(new Runnable()
            {

                @Override
                public void run()
                {
                    final int total[] = new int [1];
                    total[0] = 0;


            long start = Integer.parseInt(start_num_copy);
            long end = Integer.parseInt(end_num_copy);
            int counter = (int) (end - start);

            pr.setMax(counter);

            int i;
            for (i = 0; i <= counter && !stopCopy; i++)
            {
                total[0] += 1;

                pr.post(new Runnable() {

                    @Override
                    public void run() {

                        pr.setProgress(total[0]);
                    }
                });

                int k = 7 - String.valueOf(start + i).length();
                String zero = "0000000" ;



                String MobileNumber = start_str_copy.substring(0,4) + zero.substring(0,k) + String.valueOf(start + i);
                String DisplayName = start_str_copy.substring(0,4) + zero.substring(0,k) + String.valueOf(start + i);


            ArrayList < ContentProviderOperation > ops = new ArrayList < ContentProviderOperation > ();

            ops.add(ContentProviderOperation.newInsert(
                    ContactsContract.RawContacts.CONTENT_URI)
                    .withValue(ContactsContract.RawContacts.ACCOUNT_TYPE, null)
                    .withValue(ContactsContract.RawContacts.ACCOUNT_NAME, null)
                    .build());

            //------------------------------------------------------ Names
            if (DisplayName != null)
            {
                ops.add(ContentProviderOperation.newInsert(
                        ContactsContract.Data.CONTENT_URI)
                        .withValueBackReference(ContactsContract.Data.RAW_CONTACT_ID, 0)
                        .withValue(ContactsContract.Data.MIMETYPE,
                        ContactsContract.CommonDataKinds.StructuredName.CONTENT_ITEM_TYPE)
                        .withValue(
                        ContactsContract.CommonDataKinds.StructuredName.DISPLAY_NAME,
                        DisplayName).build());
            }

            //------------------------------------------------------ Mobile Number                     
            if (MobileNumber != null)
            {
                ops.add(ContentProviderOperation.
                        newInsert(ContactsContract.Data.CONTENT_URI)
                        .withValueBackReference(ContactsContract.Data.RAW_CONTACT_ID, 0)
                        .withValue(ContactsContract.Data.MIMETYPE,
                        ContactsContract.CommonDataKinds.Phone.CONTENT_ITEM_TYPE)
                        .withValue(ContactsContract.CommonDataKinds.Phone.NUMBER, MobileNumber)
                        .withValue(ContactsContract.CommonDataKinds.Phone.TYPE,
                        ContactsContract.CommonDataKinds.Phone.TYPE_MOBILE)
                        .build());
            }

            // Asking the Contact provider to create a new contact                 

            try 
            {
                getContentResolver().applyBatch(ContactsContract.AUTHORITY, ops);
            } 
            catch (Exception e)
            {
                e.printStackTrace();
                //Toast.makeText(this, "Exception: " + e.getMessage(), Toast.LENGTH_SHORT).show();
            } 

        }
            if (i == counter +1)
            {
                pr.post(new Runnable() {
                    public void run() {
                        pr.setVisibility(View.GONE);
                    }
                });
                btn_start_copy.post(new Runnable() {

                    @Override
                    public void run() {
                        btn_start_copy.setText("START");

                    }
                });

                isCopy = !isCopy;
            }
        }
    });copy.start();
            }
            }
            else
            {
                stopCopy = true;
                btn_start_copy.setText("START");
                pr.setVisibility(View.GONE);
            }
            isCopy = !isCopy;
        }
    });

请帮帮我。感谢