EditText 2개에 숫자(컴퓨터입장에선 문자)를 입력받아서

두가지 수를 합산하는 버튼을 만들어

3번째 EditText에 결과값을 출력하는 프로그램을 짜는건데요

주석달아서 실행해보니까 자꾸 문자를 숫자로 변환하는 과정에서 에러가 뜨더라구요.

코드 와 xml 올려드릴테니 뭐가 잘못된건지좀 봐주세요 ㅠㅠ

package exam.Ex;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class ExActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
       
       EditText first = (EditText)findViewById(R.id.num1);
        EditText second = (EditText)findViewById(R.id.num2);
       
        String first_text = first.toString();
        String second_text = second.toString();
       
        int a = Integer.parseInt(first_text);    <<<여기서부터 주석처리하면 정상적으로 실행되는데 여기서주석풀고
        int b = Integer.parseInt(second_text);
       
        int hap = a+b;
                                                                   <<여기까지 주석풀어놓으면 에러가뜹니다..문자->숫자로 바꾸는과정에서 그러는거같은데 ㅠ

        final String answer01 = String.valueOf(hap);
        final EditText hap_01 = (EditText)findViewById(R.id.sum1);
       
        Button button01 = (Button)findViewById(R.id.button1);
        button01.setOnClickListener(new View.OnClickListener(){
         public void onClick(View v){
          hap_01.setText(answer01);
         }
        });
      
        String hap_result = answer01.toString();
       
        int c = Integer.parseInt(hap_result);
        int gop = c*2;
       
        final String answer02 = String.valueOf(gop);
        final EditText gop_02 = (EditText)findViewById(R.id.sum2);
       
        Button button02 = (Button)findViewById(R.id.button2);
        button02.setOnClickListener(new View.OnClickListener(){
         public void onClick(View v){
          gop_02.setText(answer02);
         }
        });
    }
}
 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
     <LinearLayout
              android:orientation="horizontal"   
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              >
              <TextView 
                android:id="@+id/text1"            
                android:layout_width="100dp"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="첫번째 숫자:"
                />
              <EditText
                android:id="@+id/num1"
                android:orientation="vertical"   
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
               />     
      </LinearLayout>
     
          <LinearLayout
              android:orientation="horizontal"   
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              >
              <TextView     
                android:id="@+id/text2"        
                android:layout_width="100dp"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="두번째 숫자:"
                />
              <EditText
                android:id="@+id/num2"
                android:orientation="vertical"   
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
               />     
      </LinearLayout>
         <LinearLayout
              android:orientation="horizontal"   
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              >
       <Button
                android:text="합"
                android:id="@+id/button1"
                android:layout_width="110dp"
                android:layout_height="wrap_content"
                />
            <EditText
                android:id="@+id/sum1"
                android:orientation="vertical"   
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
               />
       </LinearLayout>
               <LinearLayout
              android:orientation="horizontal"   
              android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              >
       <Button
                android:text="합*2"
                android:id="@+id/button2"
                android:layout_width="110dp"
                android:layout_height="wrap_content"
                />
            <EditText
                android:id="@+id/sum2"
                android:orientation="vertical"   
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
               />
       </LinearLayout>

</LinearLayout>