안드로이드 액티비티 전환하기 문의

package com.example.customlistview03;
 
import java.util.ArrayList;
import java.util.Collections;
 
import com.example.customlistview03.SubActivity;
import com.example.customlistview03.R;
 
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
 
public class MainActivity extends Activity {
    private ListView mListView = null;
    private ListViewAdapter mAdapter = null;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        mListView = (ListView) findViewById(R.id.mList);
 
        mAdapter = new ListViewAdapter(this);
        mListView.setAdapter(mAdapter);
 
        mAdapter.addItem(getResources().getDrawable(R.drawable.korea),
                "korea",
                "인구: 5022만");
        mAdapter.addItem(getResources().getDrawable(R.drawable.china),
                "china",
                "인구: 13.57억");
        mAdapter.addItem(getResources().getDrawable(R.drawable.canada),
                "canada",
                "인구: 3516만");
        mAdapter.addItem(getResources().getDrawable(R.drawable.australia),
                "australia",
                "인구: 2313만");
        mAdapter.addItem(getResources().getDrawable(R.drawable.usa),
                "usa",
                "인구: 3.189억");
        mAdapter.addItem(getResources().getDrawable(R.drawable.italy),
                "italy",
                "인구: 5983만");
 
 
 
        mListView.setOnItemClickListener(new OnItemClickListener() {
 
            @Override
            public void onItemClick(AdapterView<?> parent, View v, int position, long id){
                ListData mData = mAdapter.mListData.get(position);
                Toast.makeText(MainActivity.this, mData.mNation, Toast.LENGTH_SHORT).show();
            }
        });
    }
 
    private class ViewHolder {
        public ImageView mIcon;
 
        public TextView mNation;
 
        public TextView mPopulation;
    }
 
    private class ListViewAdapter extends BaseAdapter {
        private Context mContext = null;
        private ArrayList<ListData> mListData = new ArrayList<ListData>();
 
        public ListViewAdapter(Context mContext) {
            super();
            this.mContext = mContext;
        }
 
        @Override
        public int getCount() {
            return mListData.size();
        }
 
        @Override
        public Object getItem(int position) {
            return mListData.get(position);
        }
 
        @Override
        public long getItemId(int position) {
            return position;
        }
 
        public void addItem(Drawable icon, String mTitle, String mDate){
            ListData addInfo = null;
            addInfo = new ListData();
            addInfo.mIcon = icon;
            addInfo.mNation = mTitle;
            addInfo.mPopulation = mDate;
 
            mListData.add(addInfo);
        }
 
        public void remove(int position){
            mListData.remove(position);
            dataChange();
        }
 
        public void sort(){
            Collections.sort(mListData, ListData.ALPHA_COMPARATOR);
            dataChange();
        }
 
        public void dataChange(){
            mAdapter.notifyDataSetChanged();
        }
 
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder;
            if (convertView == null) {
                holder = new ViewHolder();
 
                LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                convertView = inflater.inflate(R.layout.listview_item, null);
 
                holder.mIcon = (ImageView) convertView.findViewById(R.id.mImage);
                holder.mNation = (TextView) convertView.findViewById(R.id.mText);
                holder.mPopulation = (TextView) convertView.findViewById(R.id.mDate);
 
                convertView.setTag(holder);
            }else{
                holder = (ViewHolder) convertView.getTag();
            }
 
            ListData mData = mListData.get(position);
 
            if (mData.mIcon != null) {
                holder.mIcon.setVisibility(View.VISIBLE);
                holder.mIcon.setImageDrawable(mData.mIcon);
            }else{
                holder.mIcon.setVisibility(View.GONE);
            }
 
            holder.mNation.setText(mData.mNation);
            holder.mPopulation.setText(mData.mPopulation);
 
            return convertView;
        }
    }
 
    public void mOnClick(View v) {
		Intent intent = new Intent(this, SubActivity.class);
		startActivity(intent);
	}
}

package com.example.customlistview03;
 
import java.text.Collator;
import java.util.Comparator;
 
import android.graphics.drawable.Drawable;
 
public class ListData {
 
 
    public Drawable mIcon;
 
 
    public String mNation;
 
 
    public String mPopulation;
 
 
 
    public static final Comparator<ListData> ALPHA_COMPARATOR = new Comparator<ListData>() {
        private final Collator sCollator = Collator.getInstance();
 
        @Override
        public int compare(ListData mListDate_1, ListData mListDate_2) {
            return sCollator.compare(mListDate_1.mNation, mListDate_2.mNation);
        }
    };
}

package com.example.customlistview03;
 
import com.example.customlistview03.R;
 
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
 
public class SubActivity extends Activity {
 
	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
	    super.onCreate(savedInstanceState);
	    setContentView(R.layout.subactivity);
 
	    // TODO Auto-generated method stub
	}
 
	public void mOnClick(View v) {
		finish();
	}
 
}