sendWhatsapp.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        String num = "+94****525";
        String msg = "மருத்துவ ஆலோசனை தேவை";

        boolean installed = isAppInstalled("com.whatsapp");

        if(installed){
            Intent intent = new Intent(Intent.ACTION_VIEW);
            intent.setData(Uri.parse("https://api.whatsapp.com/send?phone=" + num + "&text=" + msg));
            startActivity(intent);
        }else {
            Toast.makeText(HomeActivity.this, "வட்சப் செயலியை நிறுவுக!", Toast.LENGTH_SHORT).show();
        }
    }
});



private boolean isAppInstalled(String s) {

    PackageManager packageManager = getPackageManager();
    boolean is_installed;

    try {
        packageManager.getPackageInfo(s, PackageManager.GET_ACTIVITIES);
        is_installed = true;
    } catch (PackageManager.NameNotFoundException e) {
        is_installed = false;
        e.printStackTrace();
    }

    return is_installed;
}


in Manifest file


<queries>

    <package android:name="com.whatsapp" />
    <package android:name="com.whatsapp.w4b" />

</queries>