DeviceId

package com.unique.identifyingdevices;

/**
 * Created by sahir on 31/08/16.
 */

import android.content.Context;
import android.provider.Settings;
import android.telephony.TelephonyManager;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Random;
import java.util.UUID;

public class DeviceId {

    private static String sID = null;
    private static final String INSTALLATION = "CONSTANT_INSTALLATION_APP_GENERATED_ID";
    public static final String FIXED_ANDROID_ID = "9774d56d682e549c";

    public synchronized static String getId(Context context) {

        if (sID == null) {
            File installation = new File(context.getFilesDir(), INSTALLATION);
            try {
                if (!installation.exists()) {

                    UUID deviceUuid = new UUID(getDeviceIMEI(context).hashCode(), context.getApplicationContext()
                            .getPackageName().hashCode());
                    sID = deviceUuid.toString();

                    writeInstallationFile(installation, sID);

                }
                sID = readInstallationFile(installation);

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        return sID;
    }

    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);
    }

    private static void writeInstallationFile(File installation, String id) throws IOException {
        FileOutputStream out = new FileOutputStream(installation);
        out.write(id.getBytes());
        out.close();
    }

    private static String getDeviceIMEI(Context context) {

        TelephonyManager mTelephonyManager = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
        String deviceIMEI = mTelephonyManager.getDeviceId();
        if (deviceIMEI == null || deviceIMEI.equals("")) {
            return getAndroidId(context);
        } else {
            return deviceIMEI;
        }

    }

    private static String getAndroidId(Context context) {
        String androidId = Settings.Secure.getString(context.getContentResolver(),
                android.provider.Settings.Secure.ANDROID_ID);

        if (androidId.equalsIgnoreCase(FIXED_ANDROID_ID)) {
            return getRandomID(context);
        } else
            return androidId;
    }

    private static String getRandomID(Context context) {
        // If nothing is found for this device, generate a random number, although this case is not possible.
        Random tmpRand = new Random();
        return String.valueOf(tmpRand.nextLong());
    }
}

get android device unique id