kalkulator3

package com.example.root.kalkulator;
import android.content.DialogInterface;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
  //Called when the activity is first created
  private EditText angka1;
  private EditText angka2;
  private Spinner spinOperasi;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      angka1 = (EditText)findViewById(R.id.editPertama);
      angka2 = (EditText)findViewById(R.id.editKedua);
      spinOperasi = (Spinner)findViewById(R.id.spinnerOperasi);
  }
  public void buttonHandler (View view){
      double a, b, hasil;
      if(angka1.getText().length() == 0){
          Toast.makeText(this, "Angka Pertama masih kosong", Toast.LENGTH_LONG).show();
          return;
      }
      if(angka2.getText().length() == 0){
          Toast.makeText(this, "Angka Kedua masih kosong", Toast.LENGTH_LONG).show();
          return;
      }
      a = Double.parseDouble(angka1.getText().toString());
      b = Double.parseDouble(angka2.getText().toString());
      //hasil = a + b;
      switch (spinOperasi.getSelectedItemPosition()){
          case 0 :
              hasil = a + b;
              break;
          case 1 :
              hasil = a - b;
              break;
          case 2 :
              hasil = a * b;
              break;
          case 3 :
              hasil = a / b;
              break;
          default :
              hasil = a + b;
              break;
      }
      AlertDialog.Builder builder = new AlertDialog.Builder(this);
      builder.setTitle("Hasil Operasi"+spinOperasi.getSelectedItem().toString());
      builder.setMessage("Hasil = "+String.valueOf(hasil)).setPositiveButton("OK", new DialogInterface.OnClickListener(){
          @Override
          public void onClick(DialogInterface dialog, int which){
              //TODO Auto-generated method stub
              angka1.setText("");
              angka2.setText("");
              dialog.dismiss();
          }
      });
      AlertDialog dialogHasil = builder.create();
      dialogHasil.show();
      Toast.makeText(this, "Angka Pertama masih kosong", Toast.LENGTH_LONG).show();
  }
}