How to disable back,home,multitask physical buttons?

Actually i'm developing an app and just this app should be opened on the device where is installed so i would be able to block / disable physical buttons for back,home,multitask.

I've read yet some articles about how to do it but still can't get how to implement it in my app.

The buttons i would disable are the following that you can see on the photo

//Just put below code onStart() method

@Override
    protected void onStart() {
        super.onStart();
        // start lock task mode if it's not already active
        ActivityManager am = (ActivityManager) getSystemService(
                Context.ACTIVITY_SERVICE);
        // ActivityManager.getLockTaskModeState api is not available in pre-M.
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
            if (!am.isInLockTaskMode()) {
                startLockTask();
            }
        } else {
            if (am.getLockTaskModeState() ==
                    ActivityManager.LOCK_TASK_MODE_NONE) {
                startLockTask();
            }
        }


    }