Java：找不到符号类

Question

我正在编写一个程序，它从两个文本字段获取两个值并计算其结果。

的问题是，Java编辑器显示我以下错误：

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 

这里是我的代码：

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

使用以下进口

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