关于初始化成员变量

package jxnu.edu.cn.x3321;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;

public class MainActivity extends Activity {

    //1.定义成员变量
    ExpandableListView elv;
    
    String [] group=new String[] {
            "Friends","Family","Teachers","Classmates"
    };
    String [][] members=new String[][] {
        {"Timi","Kimi","Cathy"},
        {"Lucy","Kaven","Hebe"},
        {"Selina","Ella","Bull"},
        {"Kerry","Mika","Mraz"},
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        elv=(ExpandableListView)this.findViewById(R.id.elv);
        //自定义适配器
        Myela ela=new Myela(getApplicationContext(),group,members);
        //加载适配器
        elv.setAdapter(ela);
    }

    @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;
    }

}

elv=(ExpandableListView)this.findViewById(R.id.elv);
如果这句直接接在定义变量后面就会报错的！注意注意！