How to detect if device support notch display?

You need to use the getDisplayCutout method of the WindowInsets object. This will give you a DisplayCutout object, which you can query to find the "safe" insets within the display.

The DisplayCutout class is new in API level 28, so you won't be able to do it on devices with a lower API level (you can assume that there's no notch unless it's API level >= 28).

There's a guide here.

You can get hold of the WindowInsets object by overriding the onApplyWindowInsets method of the View, or by implementing a OnApplyWindowInsetsListener class.

Some Oreo devices also have notch display if you are targeting to support all OS then you can use my solution. As per material design guidelines the status bar height for Android devices is 24dp. You can get device status bar height and device density by using the following and check if status bar height is more than 24dp. If its height is more than 24dp then it has the notch on display and then you can handle your view position as per your requirement. This will work on Oreo as well.

int statusBarHeight = 0;
int resourceId = getResources().getIdentifier("status_bar_height", "dimen", "android");
if (resourceId > 0) {
    statusBarHeight = getResources().getDimensionPixelSize(resourceId);
}

// DP to Pixels

public static int convertDpToPixel ( float dp){
    DisplayMetrics metrics = Resources.getSystem().getDisplayMetrics();
    float px = dp * (metrics.densityDpi / 160f);
    return Math.round(px);
}

// Make UI adjustments as per your requirement

if (statusBarHeight > convertDpToPixel(24)) {
    RelativeLayout.LayoutParams topbarLp = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
    topbarlp.setMargins(0, statusBarHeight, 0, 0);

    //Set above layout params to your layout which was getting cut because of notch
    topbar.setLayoutParams(topbarlp)
}