package lowmans.MySdcardWriteTest;

import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

import android.app.Activity;

import android.os.Bundle;

import android.util.Log;

public class MySdcardWriteTest extends Activity {

	final String tag = "MySdcardWriteTest";

    /** Called when the activity is first created. */

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        String path ="/sdcard/";

        File file = new File(path+"myTest.txt");

        try{

        	FileOutputStream fos = new FileOutputStream(file);

        	fos.write("this is test~!!\nThis Is Test~!!".getBytes());

        	fos.close();

        }catch(IOException e){

        	Log.i(tag , e.getMessage());

        }

    }

}

 <?xml version="1.0" encoding="utf-8"?>

<manifest package="lowmans.MySdcardWriteTest"

      android:versionCode="1"

      android:versionName="1.0" xmlns:android="http://schemas.android.com/apk/res/android">

    <application android:icon="@drawable/icon" android:label="@string/app_name"

    >

        <activity android:name=".MySdcardWriteTest"

                  android:label="@string/app_name">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

    </application>

    <uses-sdk android:minSdkVersion="4" />

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

</manifest>