how to check internal and external storage if exist

it's already explained in android documentation.

Code taken from documentation

boolean mExternalStorageAvailable = false;boolean mExternalStorageWriteable = false;String state = Environment.getExternalStorageState();if (Environment.MEDIA_MOUNTED.equals(state)) {    // We can read and write the media    mExternalStorageAvailable = mExternalStorageWriteable = true;} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {    // We can only read the media    mExternalStorageAvailable = true;    mExternalStorageWriteable = false;} else {    // Something else is wrong. It may be one of many other states, but all we need    //  to know is we can neither read nor write    mExternalStorageAvailable = mExternalStorageWriteable = false;}

I wrote a little class for that checking the storage state. Maybe it's of some use for you.

UPDATE: Cleaned up code, removed comments and made class static.

import android.os.Environment;public class StorageHelper {    private static boolean externalStorageReadable, externalStorageWritable;    public static boolean isExternalStorageReadable() {        checkStorage();        return externalStorageReadable;    }    public static boolean isExternalStorageWritable() {        checkStorage();        return externalStorageWritable;    }    public static boolean isExternalStorageReadableAndWritable() {        checkStorage();        return externalStorageReadable && externalStorageWritable;    }    private static void checkStorage() {        String state = Environment.getExternalStorageState();        if (state.equals(Environment.MEDIA_MOUNTED)) {            externalStorageReadable = externalStorageWritable = true;        } else if (state.equals(Environment.MEDIA_MOUNTED) || state.equals(Environment.MEDIA_MOUNTED_READ_ONLY)) {            externalStorageReadable = true;            externalStorageWritable = false;        } else {            externalStorageReadable = externalStorageWritable = false;        }    }}

Code from the documentation that's been simplified a bit since previous answers:

/* Checks if external storage is available for read and write */public boolean isExternalStorageWritable() {    String state = Environment.getExternalStorageState();    if (Environment.MEDIA_MOUNTED.equals(state)) {        return true;    }    return false;}/* Checks if external storage is available to at least read */public boolean isExternalStorageReadable() {    String state = Environment.getExternalStorageState();    if (Environment.MEDIA_MOUNTED.equals(state) ||        Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {        return true;    }    return false;}