Design a reservation system for restaurant

ReservationManager.java

public class ReservationManager {
	List<Reservation> reservations;
	List<Table> tables;
	Set<Customer> customers;
	private static ReservationManager instance;
	
	private ReservationManager(){
		customers = new HashSet<>();
		init();
	}
	
	public ReservationManager getInstance(){
		if(instance == null){
			instance = new ReservationManager();
		}
		return instance;
	}
	
	private void init(){
		reservations = new ArrayList<>();
		tables = new ArrayList<>();
		// todo: add different types of tables
	}
	
	public void CreateNewProfile(int customerId, String fullName, String contactInfo){
		// create profile for new customer
	}
	
	public boolean makeReservation(int customerId, LocalDate reservationTime, String otherRequirements){
		Table table = null;
		for(Table t : tables){
			if(t.isAvailable(reservationTime)){
				table = t;
				break;
			}
		}
		if(table != null){
			Reservation rsv = new Reservation(customerId, table.tableId, reservationTime, otherRequirements);
			return true;
		}
		return false;	
	}

	
	private class Table{
		int tableId;
		int numberOfSeats;
		TableType type;
		
		public Table(int id, int number, TableType type){
			this.tableId = id;
			this.numberOfSeats = number;
			this.type = type;
		}
		
		public boolean isAvailable(LocalDate reservationTime){
			// check if this table is available begin from reserve time, the default duration is 1 hour.
			return true;
		}
		
	}
	
	enum TableType{
		Booth, HighTable
	}
}

class Reservation{
	int reservationId;
	int customerId;
	int tableId;
	LocalDate creationTime;
	LocalDate reservationTime;
	String otherRequirements;
	
	public Reservation(int customerId, int tableId, LocalDate reservationTime, String otherRequirements){
		this.reservationId = reservationId;
		this.tableId = tableId;
		this.customerId = customerId;
		this.reservationTime = reservationTime;
		this.otherRequirements = otherRequirements;
	}
	
	public void udpateTable() {
		// to change the table for customer
	}
	
	public void updateTime(){
		// update the reservation time
	}
	
	public void updateRequirements(){
		// update the requirements
	}
}

class Customer{
	private int customerId;
	private String fullName;
	private String telephoneNumber;
	public Customer(int id, String name, String telePhoneNumber){
		this.customerId = id;
		this.fullName = name;
		this.telephoneNumber = telePhoneNumber;
	}
	
	public int getId(){
		return this.customerId;
	}
	
	public String getName(){
		return this.fullName;
	}
	
	public String getTeleNumber(){
		return this.telephoneNumber;
	}
	
	// update methods
}

is that the singleton pattern?

Yes it is

What is table_id? Is it unique per restaurant or unique across all restaurants?

Where is the main method? Please share it if you can.

have not main Function
please answere

having variables as static class variable would be more appropriate