public DomainLister(final int amount, final int length, String tld) {
		if (amount <= 0) {
			throw new IllegalArgumentException("invalid amount.");
		}
		if (length <= 2) {
			throw new IllegalArgumentException("invalid length.");
		}

		tld = tld.trim().toLowerCase();
		if (tld.isEmpty()) {
			throw new IllegalArgumentException("invalid tld.");
		}
		if (!tld.contains(".")) {
			tld = "." + tld;
		}

		this.amount = amount;
		this.length = length;
		this.tld = tld;
		this.whois = new WhoisLookup();
		this.gen = new DomainNameGenerator(this.length);
	}