jika app ada atau tidak

//Function 1

private boolean isAppInstalled(String packageName) {
    PackageManager pm = getPackageManager();
    boolean installed = false;
    try {
        pm.getPackageInfo(packageName, PackageManager.GET_ACTIVITIES);
        installed = true;
    } catch (PackageManager.NameNotFoundException e) {
        installed = false;
    }
    return installed;
}

//Or Function 2

public boolean isAppInstalled(String targetPackage){
    List<ApplicationInfo> packages;
    PackageManager pm = getPackageManager();
    packages = pm.getInstalledApplications(0);
    for (ApplicationInfo packageInfo : packages) {
        if(packageInfo.packageName.equals(targetPackage)) return true;
    }
    return false;
}

//USAGE

if(isAppInstalled("com.package.name")){
    //Your Code
}
else{
    startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("market://details?id=com.package.name")));
}