R.java was modified manually! Reverting to generated version!

langList = (ListView) findViewById(R.id.langList);

package com.mine.lab_2;
 
import java.util.ArrayList;
import java.util.Arrays;
 
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
 
public class MainActivity extends Activity {
    
    ArrayList<String> langNames;
    EditText edit1;
    ListView langList;
    ArrayAdapter<String> listAdapter;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        langNames = new ArrayList<String>(Arrays.asList("Basic", "Pascal", "C", "C++", "C#", "Java",
        "PHP", "Python", "Objective C"));
        edit1=(EditText)findViewById(R.id.editText1);
        langList = (ListView) findViewById(R.id.langList);
        listAdapter = new ArrayAdapter<String> ( this, android.R.layout.simple_list_item_1, langNames);
        langList.setAdapter(listAdapter);
        Button okButton=(Button)findViewById(R.id.button1);
                
        okButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                langNames.add(0, edit1.getText().toString());
                listAdapter.notifyDataSetChanged();
            }
        });
    }
 
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
 
}