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I was trying to make an app that can find the IP address of a device connected to my android phone's hotspot using it's MAC address. I know this can be done using ARP tables but I just don't know how. I'm using android studio with java and my device is running android 10. Please help.

MohanKumar
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sahil bhatnagar
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  • The question doesn't appear to include any attempt at all to solve the problem. Please edit the question to show what you've tried, and show a specific roadblock you're running into with [Minimal, Complete, and Verifiable example](https://stackoverflow.com/help/mcve). For more information, please see [How to Ask](https://stackoverflow.com/help/how-to-ask). – Andreas Oct 18 '19 at 08:28
  • The thing is, i don't have any idea how I'm supposed to do it, so I can't even try – sahil bhatnagar Oct 18 '19 at 08:49
  • Do your research first then. You know that this can be done using ARP tables, so start researching from there. StackOverflow is a site for specific programming questions and answers and as of now, your question is too broad – Andreas Oct 18 '19 at 08:50

1 Answers1

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Here's how it's implemented in AndroidNetworkTools library, which worked fine for me:

 /**
 * Returns all the IP/MAC address pairs currently in the ARP cache (/proc/net/arp).
 */
public static HashMap<String, String> getAllIPAndMACAddressesInARPCache() {
    HashMap<String, String> macList = new HashMap<>();
    for (String line : getLinesInARPCache()) {
        String[] splitted = line.split(" +");
        if (splitted.length >= 4) {
            // Ignore values with invalid MAC addresses
            if (splitted[3].matches("..:..:..:..:..:..")
                    && !splitted[3].equals("00:00:00:00:00:00")) {
                macList.put(splitted[0], splitted[3]);
            }
        }
    }
    return macList;
}

/**
 * Method to read lines from the ARP Cache
 */
private static ArrayList<String> getLinesInARPCache() {
    ArrayList<String> lines = new ArrayList<>();
    BufferedReader br = null;
    try {
        br = new BufferedReader(new FileReader("/proc/net/arp"));
        String line;
        while ((line = br.readLine()) != null) {
            lines.add(line);
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            if (br != null) {
                br.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return lines;
}
chehonte
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