// High performance
public static String getProcessName() {
  try {
    File file = new File("/proc/" + android.os.Process.myPid() + "/" + "cmdline");
    BufferedReader mBufferedReader = new BufferedReader(new FileReader(file));
    String processName = mBufferedReader.readLine().trim();
    mBufferedReader.close();
    return processName;
  } catch (Exception e) {
    e.printStackTrace();
    return null;
  }
}

// Normal
public static String getProcessName(Context cxt, int pid) {
    ActivityManager am = (ActivityManager) cxt.getSystemService(Context.ACTIVITY_SERVICE);
    List<RunningAppProcessInfo> runningApps = am.getRunningAppProcesses();
    if (runningApps == null) {
        return null;
    }
    for (RunningAppProcessInfo procInfo : runningApps) {
        if (procInfo.pid == pid) {
            return procInfo.processName;
        }
    }
    return null;
}