android:file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/name" />

    <EditText
        android:id="@+id/fname"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:inputType="text" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/content" />

    <EditText
        android:id="@+id/fcontent"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:inputType="text"
        android:minLines="6" />

    <Button
        android:id="@+id/store"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/store" />

</LinearLayout>

package com.example.service;

import java.io.FileOutputStream;

import android.content.Context;

public class FileService {
	private Context context;
    public FileService(Context context) {
		this.context = context;
	}
	public void save(String filename,String content)throws Exception{
    	FileOutputStream outputStream=context.openFileOutput(filename, Context.MODE_PRIVATE);
    	outputStream.write(content.getBytes());
    	outputStream.close();
    }
}

package com.example.file;

import com.example.service.FileService;

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

public class FileActivity extends Activity {

	private static final String TAG="FileActivity";
	private FileService fileService;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_file);
	fileService=new FileService(this);
	Button button=(Button)this.findViewById(R.id.store);
	button.setOnClickListener(new View.OnClickListener() {
		
		@Override
		public void onClick(View v) {
            EditText filenameText=(EditText)findViewById(R.id.fname);
            EditText contentText=(EditText)findViewById(R.id.fcontent);
            String filename=filenameText.getText().toString();
            String content=contentText.getText().toString();
            try {
				fileService.save(filename, content);
				Toast.makeText(FileActivity.this, R.string.success,Toast.LENGTH_LONG).show();
			} catch (Exception e) {
				Log.e(TAG,e.toString());
				Toast.makeText(FileActivity.this, R.string.fail,Toast.LENGTH_SHORT).show();
			}
		}
	});
	}
}