Java tutorial
//package com.java2s; //License from project: Open Source License import android.content.Context; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.RandomAccessFile; import java.util.UUID; public class Main { private static String sID = null; private static final String INSTALLATION = "INSTALLATION"; public synchronized static String id(Context context) { if (sID == null) { File installation = new File(context.getFilesDir(), INSTALLATION); try { if (!installation.exists()) writeInstallationFile(installation); sID = readInstallationFile(installation); } catch (Exception e) { // throw new RuntimeException(e); sID = "1234567890"; } } return sID; } private static void writeInstallationFile(File installation) throws IOException { FileOutputStream out = new FileOutputStream(installation); String id = UUID.randomUUID().toString(); out.write(id.getBytes()); out.close(); } private static String readInstallationFile(File installation) throws IOException { RandomAccessFile f = new RandomAccessFile(installation, "r"); byte[] bytes = new byte[(int) f.length()]; f.readFully(bytes); f.close(); return new String(bytes); } }