How to detect that a device is rooted in Android

RootUtil.java

package com.booknara.android;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;

import android.util.Log;
// Reference : http://stackoverflow.com/a/8097801/2015075

public class RootUtil {
	private static String TAG = RootUtil.class.getName();

    public boolean isDeviceRooted() {
        return checkRootMethod1() || checkRootMethod2() || checkRootMethod3();
    }

    public boolean checkRootMethod1() {
        String buildTags = android.os.Build.TAGS;
        return buildTags != null && buildTags.contains("test-keys");
    }

    public boolean checkRootMethod2() {
        try {
            File file = new File("/system/app/Superuser.apk");
            return file.exists();
        } catch (Exception e) {} return false;
    }

    public boolean checkRootMethod3() {
        return new ExecShell().executeCommand(SHELL_CMD.check_su_binary)!=null;
    }

    public enum SHELL_CMD {
        check_su_binary(new String[] { "/system/xbin/which", "su" });

        String[] command;

        SHELL_CMD(String[] command) {
            this.command = command;
        }
    }

    public class ExecShell {
        public ArrayList<String> executeCommand(SHELL_CMD shellCmd) {
            String line = null;
            ArrayList<String> fullResponse = new ArrayList<String>();
            Process localProcess = null;
            try {
                localProcess = Runtime.getRuntime().exec(shellCmd.command);
            } catch (Exception e) {
                return null;
            }
            BufferedWriter out = new BufferedWriter(new OutputStreamWriter(
                    localProcess.getOutputStream()));
            BufferedReader in = new BufferedReader(new InputStreamReader(
                    localProcess.getInputStream()));
            try {
                while ((line = in.readLine()) != null) {
                    Log.d(TAG, "--> Line received: " + line);
                    fullResponse.add(line);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            Log.d(TAG, "--> Full response was: " + fullResponse);
            return fullResponse;
        }
    }
}

checkRootMethod3 is wrong. You have to check for /su in the output... on Samsung S7 it outputs 1 and return becomes true. Learn the hardway