问Java blueJ类成员/ Lan

EN

public class Member 
{

    private String name;
    private String alias;
    public int balance;

    /**
     * Constructor for objects of class Member
     */
    public Member(String fullName, String nickname)
    {
        this.name = fullName;
        this.alias = nickname;
        this.balance = 0;
    }
    public void setBalance(int account)
    {
        if(account > 0)
        {
            balance = balance + account;
        }
        else
        {
            System.out.println("You have not entered a valid number");
        }
    }
}

import java.util.ArrayList;

public class Lan
{
    private ArrayList<Member> members;

    public Lan()
    {
      members = new ArrayList<Member>();
    }

    public void addMember(Member newMember)
    {
        if(balance >= 200)
        {
            this.members.add(newMember);
        }
        else
        {
            System.out.println("You dont have enough money to enter");
        }

    }
}