Java：找不到符號類

Question

我正在編寫一個程序，它從兩個文本字段獲取兩個值並計算其結果。

的問題是，Java編輯器顯示我以下錯誤：

cannot find symbol class EditText 
cannot find symbol class Button 
cannot find symbol class string 
cannot find symbol class variable integer 
cannot find symbol class integer 

這裏是我的代碼：

public class MainActivity extends AppCompatActivity 
{ 
    EditText firstNumber; 
    EditText secondNumber; 
    Button btnAdd; 
    TextView total; 


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

     firstNumber = (EditText)findViewById(R.id.firstNumber); 
     secondNumber = (EditText)findViewById(R.id.secondNumber); 
     btnAdd = (Button)findViewById(R.id.btnAdd); 
     total = (TextView)findViewById(R.id.total); 
    } 

    public void btnAdd_Click(View view) 
    { 
     string getfirstNumber = firstNumber.getText().toString(); 
     string getsecondNumber = secondNumber.getText().toString(); 
integer totalResult = integer.parseInt(getfirstNumber) + integer.parseInt(getsecondNumber); 
total.setText("Total = " + integer.toString(totalResult)); 

    } 
} 

Answer 1

使用以下進口

import android.widget.Button; 
import android.widget.EditText;