Shareholders

That depends on what you mean by "bought out".  If the buyer buys the assets of the public corporation, the money would be paid out to creditors of the corporation and the remainder distributed to the shareholders.  If the buyer buys the stock of the corporation, it is buying the stock from shareholders, who will be paid for their stock if they agree to sell.  If not, they would remain shareholders of the corporation.  If the corporation is merged into another, there will be a forumula in the offering documents which will set forth the conversion rate for stock, i.e. 5 shares of the original corporation's stock would be converted into one share of the buying corporation's stock.