Android Toast not showing up

I really don't know what caused this, but Toasts in my application are no longer showing up.

How do I display a Toast: Toast.makeText(getApplicationContext(), "Toast...", Toast.LENGTH_SHORT).show();

I've checked Toast.java and it seems that there are some symbols that cannot be resolved: IntDef, INotificationManager, ITransientNotification.

I have tried rebuilding and cleaning up the project but no success.

EDIT: NumberList activity code:

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class NumberList extends Activity implements OnClickListener{
private RemindersDbAdapter mDbAdapter;
private EditText numbr;
private EditText name;
private Button btnAdd;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.list_layout);
    mDbAdapter=new RemindersDbAdapter(this);
    mDbAdapter.open();

    numbr=(EditText) findViewById(R.id.editNumber);
    name = (EditText) findViewById(R.id.editName);

   btnAdd=(Button) findViewById(R.id.btnSave);
   btnAdd.setOnClickListener(this);
}

public void onClick(View v) {


    switch (v.getId()) {
    case R.id.btnSave:

        if((numbr.getText().toString()!=null)&&(numbr.getText().toString().length()>=3)&&(numbr.getText().toString().length()<=20)) {
            mDbAdapter.createReminder(numbr.getText().toString() ,  name.getText().toString(), "");
            mDbAdapter.close();
            finish();
        }

        else {
            Toast.makeText(getApplicationContext(), "Please enter a correct number", Toast.LENGTH_SHORT).show();

        }

    default:
        break;
    }
}

@Override
protected void onDestroy() {
    // TODO Auto-generated method stub
    super.onDestroy();
    mDbAdapter.close();

}
}