import javax.swing.JOptionPane;
import java.awt.*;
import java.awt.event.*;

public class Reservations extends Frame implements ActionListener
{
    Color lightRed = new Color(255, 90, 90);
    Color lightGreen = new Color(140, 215, 40);

    Rooms room = new Rooms(5,3);

    Panel roomPanel = new Panel();
        TextArea roomDisplay[] = new TextArea[9];

    Panel buttonPanel = new Panel();
        Button bookButton = new Button("Book Room");

    Panel inputPanel = new Panel();
        Label custNameLabel = new Label("Name");
        TextField nameField = new TextField(15);
        Label custPhoneLabel = new Label("Phone Number");
        TextField phoneField = new TextField(15);
        Label amountLabel = new Label("Amount Outstanding");
        TextField amountField = new TextField(15);
        Label numLabel = new Label("Number in Party");
        Choice numberOfGuests = new Choice();
            CheckboxGroup options = new CheckboxGroup();
                Checkbox nonSmoking = new Checkbox("Nonsmoking",false,options);
                Checkbox smoking = new Checkbox("Smoking",false,options);
                Checkbox hidden = new Checkbox("",true,options);

    public Reservations()
    {
        this.setLayout(new BorderLayout());
            roomPanel.setLayout(new GridLayout(2,4,10,10));
            buttonPanel.setLayout(new FlowLayout());
            inputPanel.setLayout(new FlowLayout());


        for (int i=1; i<9; i++)
        {
            roomDisplay[i] = new TextArea(null,3,5,3);
            if(i<6)
                roomDisplay[i].setText("Room"+ i + "Nonsmoking");
            else
                roomDisplay[i].setText("Room"+ i + "Smoking");
            roomDisplay[i].setEditable(false);
            roomDisplay[i].setBackground(lightGreen);
            roomPanel.add(roomDisplay[i]);

        }

        buttonPanel.add(bookButton);

        inputPanel.add(custNameLabel);
        inputPanel.add(nameField);
        inputPanel.add(custPhoneLabel);
        inputPanel.add(phoneField);
        inputPanel.add(amountLabel);
        inputPanel.add(amountField);
        inputPanel.add(numLabel);
        inputPanel.add(numberOfGuests);
            for(int i=1; i<=4;i++)
                numberOfGuests.add(String.valueOf(i));
        inputPanel.add(nonSmoking);
        inputPanel.add(smoking);

        add(buttonPanel, BorderLayout.SOUTH);
        add(inputPanel, BorderLayout.CENTER);
        add(roomPanel, BorderLayout.NORTH);

        bookButton.addActionListener(this);

        addWindowListener(
            new WindowAdapter()
            {
                public void windowClosing(WindowEvent e)
                {
                    System.exit(0);
                }
            }
            );
        }

        public static void main(String[] args)
        {
            Reservations f = new Reservations();
            f.setBounds(200,200,600,300);
            f.setTitle("Hotel Reservations");
            f.setVisible(true);
        }

        public void actionPerformed(ActionEvent e)
        {
            if (hidden.getState())
            {
                JOptionPane.showMessageDialog(null,"You must select Nonsmoking or smoking.","Error",JOptionPane.ERROR_MESSAGE);
            }

            else
            {
                int available = room.bookRoom(smoking.getState());

                if (available > 0)
                {
                    roomDisplay[available].setBackground(lightRed);
                    roomDisplay[available].setText(
                                                    roomDisplay[available].getText() +
                                                    "\n" +
                                                    nameField.getText() +
                                                    "\n" +"R"+"\n"+
                                                    amountField.getText()+
                                                    "Outstanding"+
                                                    phoneField.getText() +
                                                    "\nparty of " +
                                                    numberOfGuests.getSelectedItem()
                                                );

                clearFields();
            }

            else
            {
                if (smoking.getState())
                    JOptionPane.showMessageDialog(null,"Smoking is full","Error",JOptionPane.INFORMATION_MESSAGE);
                else
                    JOptionPane.showMessageDialog(null,"Nonsmoking is full. ","Error",JOptionPane.INFORMATION_MESSAGE);
                hidden.setState(true);
            }
        }
    }

    void clearFields()
    {
        nameField.setText("");
        phoneField.setText("");
        amountField.setText("");
        numberOfGuests.select(0);
        nameField.requestFocus();
        hidden.setState(true);
    }
}

Source Code For rooms class

ublic class Rooms
{
    //declare class variables
    int numSmoking;
    int numNonSmoking;
    boolean occupied[];

    public Rooms(int non, int sm)
    {
        occupied = new boolean[sm+non];
        for(int i=0; i<(sm+non); i++)
        occupied[i] = false;
        numSmoking = sm;
        numNonSmoking = non;
    }

    public int bookRoom(boolean smoking)
    {
        int begin, end, roomNumber=0;

        if(!smoking)
        {
            begin = 0;
            end = numNonSmoking;
        }

        else
        {
            begin = numNonSmoking;
            end = numSmoking+numNonSmoking;
        }

        for(int i=begin; i<end; i++)
        {
            if(!occupied[i])
            {
                occupied[i] = true;
                roomNumber = i+1;
                i = end;
            }
        }
        return roomNumber;
    }
}